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CONTEIBUTIONS  TO  THE  GENETICS  OF 
DROSOPHILA  MELANOGASTER, 


I.  THE  ORIGIN  OF  GYNANDROMORPHS. 
By  T.  H.  Morgan  and  C.  B.  Bridges. 


II.  THE   SECOND    CHROMOSOME   GROUP   OF   MUTANT 

CHARACTERS. 

By  C.  B.  Bridges  and  T.  H.  Morgan. 


III.  INHERITED  LINKAGE  VARIATIONS  IN  THE  SECOND 

CHROMOSOME. 

By  a.  H.  Sturtevant. 


IV.  A  DEMONSTRATION  OF  GENES  MODIFYING  THE 

CHARACTER  "NOTCH." 

By  T.  H.  Morgan. 


J   C    4,     *  ^       ,    ..  »  •     .  -> 

I        .1      ""s  * 


, ,  > )  >  1 , ) ) '  1 


Published  by  the  Carnegie  Institution  of  Washington 

Washington,  1919 


CARNEGIE  INSTITUTION  OF  WASHINGTON 

Publication  No.  278 


Kx 


L  K      K  « 

C      C  4 

1   C     t       t  1  « 


*       %      c   t   ^      c 

C    t    (  4      (.  C       c 


PRESS  OF  GIBSON  BROS,   INC. 
WASHINGTON,  D.  C. 


CONTENTS. 


I.  The  Origin  of  Gynandromorphs.     By  T.  H.  Morgan  and  C.  R.  Bridge; 


PAGE. 
S 1 


Frequency  of  Occurrence  of  Gynandromorphs 

Relative  J^equency^  of   Elimination    of    the    Matcrnai'  and'  Paternal '" Sex 

Distribution    of  Segmentation"  Nuclei 'as  deduced 'from'  Distribution  of'the  ^^ 

Characters  of  Gynandromorphs v> 

Starting  as  a  Male  vs.  Starting  as  a  Female ,^ 

Cytological  Evidence  of  Chromosomal  Elimination.. \\ 

Earlier  Hypotheses  to  explain  Gynandromorphs. ...    \t 

The  Origin  of  the  Germ-cells  in  FUes ^^ 

Courtship  of  Gynandromorphs o 

Phototropism  in  Mosaics  with  one  White  and  one  Red  Eye 9? 

Sex-limited  Mosaics " ^'^ 

Somatic  Mosaics _\ '^^ 

Somatic  Mutation ^^ 

Mosaics  in  Plants ^'^ 

Classification  and  description  of  Gynandromorphs  oi  Drosophila 11 

Gynandromorphs  approximately  bilateral ^J 

Gynandromorphs  mainly  female ^f 

Gynandromorphs  mainly  male y.  ^ ^ 

Gynandromorphs  roughly  "fore-and-aft" ^ 

Gynandromorphs  produced  by  XX Y  females. ... „ 

Gynandromorphs  of  complex  type [    \ Jt 

Special  Cases ^^ 

Gynandromorphs  with  incomplete  data ^I 

Drosophila  Gynandromophs  previously  published 70 

Gynandromorphs  and  Mosaics  in  Bees If 

Gynandromorphs  in  Lepidoptera ot 

Other  Insects «. 

Spiders '.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'..'. 94 

Crustacea „_ 

Molluscs ■''.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'.'..'. q? 

Echinoderms no 

Vertebrates r»Q 

Fishes y^y^y.'.'.'.'.'.'.'.'.'.'.'.'.'..'. it 

Amphibia qo 

Reptiles .  ^, 

Birds yyyyyyy.y:::::::::::.: Z 

Mammals — Man -.f^f. 

Is  Cancer  a  Somatic  Mosaic? ' .' j"^ 

Is  the  Freemartin  a  Gynandromorph? 1  JJn 

Summary p'' 

Literature  Cited JP 

116 

II.  The  Second  Chromosome  Group  of  Mutant  Characters.     By  C.  B.  Bridges  and 

T.  H.  Morgan .  „„ 

Introduction "  "  ' |^^ 

Chronological  hst  of  the  II  Chromosome  Mutations 1 2fi 

Map  of  Chromosome  II ,0^ 

Speck ;:;;;;;; 127 

Ohve J28 

Truncate J^J 

Truncate  Lethal ti^ 

Snub .y.'.''.'.y.'.'''.'.'.'.'.'.'.'.'.'.'.'.'.'.'.[ HO 

Truncate  Intensification  by  Cut 143 

III 


IV  CONTENTS. 

PAGE. 

II.  The  Second  Chromosome  Group  of  Mutant  Characters — continued. 

Black 144 

Balloon .' 148 

Vestigial 150 

Blistered 155 

The  Semi-Dominance  of  Blistered — Free-Vein 158 

Jaunty ■. 160 

A  Mutating  Period  for  Jaunty 161 

Curved 164 

Purple 169 

The  Differentiation  of  Purple  by  Vermilion — Disproportional  Modification .  170 

No  Crossing  Over  in  the  Male 174 

The  Inviability  of  Vestigial — Prematuration,  Repugnance,  Lethals 177 

The  Purple  " Epidemic"—" Mutating  Periods" 178 

Balanced  Inviability,  Complementary  Crosses 181 

The  Variation  of  Crossing  Over  with  Age 183 

Coincidence 188 

The  Relation  between  Coincidence  and  Map  Distance 188 

Special  Problems  Involving  Purple — Age- Variations,  Coincidence,  Tempera- 
ture-Variations, Cross-Over  Mutations,  Progeny  Test  for  Crossing-Over  193 

Strap 200 

Arc 202 

Gap 208 

Antlered 211 

Dachs 216 

Streak 222 

Dominance  and  Lethal  Effect  of  Streak,  Parallel  to  Yellow  Mouse 223 

Comma 228 

Morula 230 

Female  Sterility  of  Morula 230 

Apterous • 236 

Cm  and  Ciir 239 

Cream  11 239 

Trefoil 244 

Cream  b 245 

Pinkish 247 

The  Double-Mating  Method 248 

Plexus 251 

Limited 254 

Confluent 255 

Confluent  Virilis 257 

Fringed 257 

Star 259 

Lethal  Nature  of  the  Homozygous  Star 260 

Crossing  Over  in  the  Male 263 

Nick 273 

Vestigial-Nick  Compound 275 

Dachs-Lethal 277 

Dachs-Deficiency? 278 

Balanced  Lethals 279 

Squat 283 

Lethal  Ila 286 

Telescope 291 

Second  Chromosome  Modifiers  for  Dichaite  Bristle  Number 293 

Dachsoid 294 

The  Construction  of  the  Map  of  the  Second  Chromosome 297 

Summary  of  Available  Data  on  Crossing  Over  in  the  Second  Chromosome 298 

Constructional  Map 302 

Working  and  Valuation  Map 303 

Bibliography 304 


CONTENTS.  V 

PAOE. 

III.  Inherited  Linkage  Variations  in  the  Second  Chromosome.    By  A.  11.  Sturtevant.  305 

Introduction 307 

" Nova  Scotia"  Chromosome 307 

Tests  of  Cross-Overs 312 

Right-hand  end  of  Nova  Scotia  Chromosome  (C//  r) 313 

Left-hand  end  of  Nova  Scotia  Chromosome  (C//  i) 316 

Homozygous  Cii  r 319 

With  Cm 319 

Without  Cn 321 

No  Tests  of  Homozygous  Cn  l 322 

Tests  Showing  No  Crossing-Over  in  Males 322 

Constitution  of  the  Nova  Scotia  Stock 322 

Another  Second-Chromosome  Linkage  Variation 324 

Comparison  with  Results  obtained  from  Cm 325 

Discussion 327 

Summary 330 

Appendix 331 

Literature  Cited 341 

IV.  A  Demonstration  of  Genes  Modifying  the  Character  "Notch."     By  T.  H.  Morgan  343 

Variation  of  Notch 346 

The  Problem 347 

Condition  of  Stock  before  Selection 348 

Selection  of  Females  having  Notch  in  one  Wing  only 349 

Selection  of  Somatically  Normal  Winged  Females  that  are  Genetically  Notched 

Females 350 

Duplicate  Selection  Experiment 355 

Localization  of  the  Gene  for  Notch 358 

The  Indentification  of  the  Modifying  Genes 361 

Short  Notch 364 

First  Test 366 

Second  Test 367 

Thh-d  Test 368 

Fourth  Test  (for  fourth-chromosome  modifiers) 369 

Recombination  of  Bent  and  Short  Notch 370 

,    Crosses  between  Short  Notch  and  Other  Stocks 371 

Short  Notch  by  Star  Dichsete 372 

Short  Notch  by  Eosin  Ruby  Forked 372 

Classification  of  Types  of  Notch 376 

Aberrant  Notch  Wings 379 

Deformed  Eyes 379 

Little  Eyes 381 

High  Sex-ratios  Caused  by  Lethals 381 

Other  Characters  that  Look  Something  Like  Notch 382 

Gynandromorph;  Notch  Eosin  Ruby 384 

Summary 387 


I. 


THE  OBIGIN  OF  GYNANDEOMORPHS. 


By  T.  H.  Morgan  and  C.  B.  Bridges. 

With  four  plates  and  seventy  text-figures. 


I.    THE  ORIGIN  OF  GYMNDROMORPHS. 


By  T.  H,  Morgan  and  C.  B.  Bridges. 


INTRODUCTION  AND  GENERAL  DISCUSSION. 

The  sharp  distinction  into  two  kinds  of  individuals,  males  and 
females,  characteristic  of  so  many  animals,  is  occasionally  done  away 
with  when  an  individual  appears  that  bears  the  structures  peculiar  to 
the  male  in  some  parts  and  to  the  female  in  other  parts  of  the  body. 
Such  an  individual  may  show  not  only  the  secondary  sexual  differences 
(either  sex-limited  or  sex-linked)  of  male  and  female,  but  gonads  and 
genitalia  of  both  kinds  as  well.  We  speak  of  these  as  gynandromorphs. 
The  union  of  the  two  sexes  in  a  single  individual  shows  how  far  the 
characteristics  normally  associated  with  one  sex  alone  are  compatible 
with  the  presence  in  another  part  of  the  same  body  of  somatic  structures 
and  reproductive  organs  of  the  opposite  sex.  In  a  word,  how  far  each 
is  independent  of  sex  hormones.  But  the  chief  importance  of  these 
rare  combinations  lies  in  the  opportunity  they  furnish  for  analysis  of 
the  changes  in  the  hereditary  mechanism  of  sex  determination  that 
makes  such  combinations  possible.  This  evidence  is  chiefly  derived 
from  gynandromorphs  that  are  also  hybrids.  Such  individuals  may 
combine  not  only  male  and  female  sex  differences,  but  the  character- 
istic racial  differences  as  well.  Whether  gynandromorphs  arise  more 
frequently  in  hybrids  or  whether  it  is  only  that  their  detection  is  easier 
under  such  circumstances  will  be  discussed  later.  The  occurrence  of 
hybrid  gynandromorphs  offers  at  any  rate  a  unique  opportunity  to 
discover  the  method  of  origin  of  such  kinds  of  individuals. 

In  hybrid  gynandromorphs  the  differences  that  are  shown  may  be 
due  to  genes  carried  by  the  sex  chromosomes.  Most  of  the  gynandro- 
morphs of  Drosophila  belong  to  this  category.  In  many  cases,  how- 
ever, especially  in  other  insects,  it  is  not  known  whether  the  differences 
shown  by  the  hybrid  gynandromorph  are  due  to  the  sex  chromosomes 
or  to  other  chromosomes,  either  because  the  ancestry  of  the  gynandro- 
morph is  unknown  or  because  the  method  of  inheritance  of  the  gene 
is  unknown.  There  are,  however,  some  very  rare  cases  in  Drosophila 
in  which  the  characters  involved  are  probably  autosomal  and  the 
individual,  while  showing  its  dual  parentage  in  different  parts  of  the 
body,  is  not  a  sex-mosaic.  It  may  be  convenient  to  designate  such 
types  as  mosaics,  while  the  sex-mosaics  may  be  designated  by  the 
more  special  term  gynandromorphs. 

In  our  work  on  Drosophila  melanogaster  (ampelophila)  a  large  number 
of  gynandromorphs  and  mosaics  have  appeared,  and  since  the  first 


THE   ORIGIN   OF   GYNANDROMORPHS. 


description  of  a  few  of  them  was  published  we  have  continued  to  keep 
records  of  their  occurrence.  Others,  too,  working  with  our  mutant 
types  have  found  them,  and  a  few  have  been  described  by  Dexter, 
Duncan,  and  Hyde.  We  soon  reahzed  that  they  occurred  with  suffi- 
cient frequency  to  make  it  possible  to  devise  experiments  of  a  sort  to 
furnish  the  long-sought  criterion  as  to  the  most  common  method  of  their 
occurrence.  It  is  this  evidence  on  which  we  wish  now  to  lay  chief 
emphasis. 

The  ordinary  gynandromorph  is  an  animal  that  is  male  on  one  side 
of  the  body  and  female  on  the  other.  The  reproductive  organs, 
gonads,  and  ducts  may  or,  in  bees  at  least,  may  not  show  a  corre- 
sponding difference.  A  typical  case  of  a  gynandromorph  that  is 
bilateral,  at  least  superficially,  is  represented  in  plate  1,  figure  1.  For 
a  long  time  it  has  been  recognized  that  bilateral  gynandromorphism 
is  only  one  kind  of  abnormal  distribution  of  the  sex  characters;  even 
in  the  classical  case  of  the  Eugster  bees  (see  p.  74)  other  distributions 
of  the  characters  were  recorded.  In  the  fly  represented  in  plate  3,  fig- 
ure 2,  the  upper  part  of  the  abdomen  is  female,  but  the  lower  side  of  the 
abdomen,  notably  the  external  genitalia,  are  male.  In  the  individual 
represented  in  plate  3,  figure  5,  the  left  anterior  side  of  the  head  is 
male,  the  right  fe- 
male, while  the  left 
posterior  parts  of  the 
body  are  female,  the 
right  male.  Other 
cases  will  be  described 
later  in  which  even 
more  irregular  and 
complex  distributions 
of  male  and  female 
parts  exist. 

Before  discussing 
these  and  other  cases 

in  detail,  it  may  be  well  to  give  three  of  the  most  recent  interpreta- 
tions of  gynandromorphism  resting  on  a  chromosomal  basis  and  the 
criteria  by  which  the  validity  of  each  has  been  tested. 

In  1888  Boveri  suggested  that  on  rare  occasions  a  spermatozoon, 
on  entering  the  egg,  might  be  delayed  in  its  penetration  to  the  vicinity 
of  the  egg-nucleus,  and  the  latter  might  meanwhile  have  begun  to 
divide,  so  that  the  sperm-nucleus  came  to  unite  with  only  one  of  its 
halves.  In  consequence,  two  kinds  of  nuclei  would  be  produced  in 
the  embryo  (text  fig.  1  a)  .  The  nuclei  that  come  from  the  sperm  plus 
the  half  egg-nucleus  would  be  diploid.  If,  as  in  the  bee,  one  nucleus 
stands  for  the  male  and  two  for  the  female,  it  follows  in  such  cases 
that  all  those  parts  of  the  body  whose  nuclei  are  derived  from  the 


Text-figure  1. 


THE    ORIGIN   OF   GYNANDROMORPHS.  5 

single  (haploid)  nucleus  would  be  male,  all  those  from  the  double 
(diploid)  would  be  female.  Moreover,  if  the  two  differ  in  one  or  more 
characters,  the  male  parts  of  the  gynandromorph  should  be  expected  to 
be  like  the  mother,  i.  e.,  maternal,  and  the  female  parts  should  be 
paternal  if  the  paternal  characters  involved  are  dominant.  The  pos- 
sibiHty  of  testing  Boveri's  hypothesis  was  pointed  out  by  one  of  us 
(Morgan)  in  1905,  and  a  test  case  was  apparently  furnished  by  a  hybrid 
gynandromorph  of  the  silkworm  moth  described  by  Toyama.  The 
result  was  not  in  harmony  with  Boveri's  hypothesis,  but  since  the 
relation  of  one  or  of  two  nuclei  to  sex  was  not  then  known  for  moths, 
the  case  is  not  decisive,  as  will  be  shown  more  at  length  later.  On  the 
other  hand,  Boveri's  discovery  of  some  preserved  specimens  of  the 
original  Eugster  gynandromorph  bees  and  his  analysis  of  their  hybrid 
characters  seemed  to  show  that  the  condition  of  these  bees  was  com- 
patible with  his  theory.  This  evidence  will  also  be  taken  up  more  fully 
later.  We  may  anticipate  our  account  of  hybrid  gynandromorphs  of 
Drosophila  and  state  that  they  furnish  direct  evidence  against  Boveri's 
hypothesis,  for  these  flies  at  least. 

In  1905  Morgan  suggested  an  alternative  hypothesis  based  on  the 
fact  that  more  than  one  spermatozoon  had  been  found  to  enter  the 
bee's  eggs.  Should  one  only  of  these  sperm-nuclei  unite  with  the 
egg-nucleus,  the  combination  would  give  rise  to  the  diploid  cells  of 
the  embryo,  while  if  a  second  (or  a  third,  etc.)  sperm-nucleus  should 
develop  it  would  give  rise  to  haploid  cells  in  the  rest  of  the  embryo 
(fig.  1  b)  .  On  this  view  the  haploid  cells  should  be  paternal  and  pro- 
duce male  parts,  and  the  diploid  cells  maternal  and  produce  female 
parts,  which  is  exactly  the  reverse  relation  in  regard  to  parental 
origin  of  the  male  and  female  parts  from  that  expected  on  Boveri's 
hypothesis.  A  decision  as  to  which  view  is  correct  might  be  reached 
in  any  special  case  in  which  sex-linked  characters  enter  from  the 
paternal  and  maternal  sides.  As  will  be  shown  later,  some  of  the 
evidence  from  the  Drosophila  gynandromorphs  is  incompatible  with 
this  hypothesis  of  Morgan. 

A  third  hypothesis  that  grew  out  of  the  work  done  in  this  labora- 
tory was  published  in  1914  by  Morgan,  based  on  evidence  from  the 
Drosophila  cases.  On  this  view  the  gynandromorphs  are  due  to  an 
elimination  of  one  of  X  chromosomes,  usually  at  some  early  division  of 
the  segmentation-nuclei.  Rarely,  in  consequence  of  a  delay  in  the  divi- 
sion of  one  of  the  X  chromosomes,  one  of  the  daughter-halves  fails  to 
reach  its  pole  and  is  lost  in  the  mid-plate  or  in  the  cell-wall  (fig.  1  c). 
As  a  result,  the  embryo  comes  to  carry  two  kinds  of  nuclei,  one  kind 
containing  one  X  and  the  other  kind  two  X  chromosomes.  The 
critical  evidence  in  favor  of  this  interpretation  is  found  in  the  presence 
on  both  sides  of  the  gynandromorph  of  other  mutant  characters  whose 
genes  are  not  in  the  X  chromosomes,  but  in  autosomes.     If,  for  example, 


6  THE    ORIGIN   OF   GYNANDROMORPHS. 

the  mother  contains  a  mutant  gene  in  one  of  her  autosomes  and  the 
father  contains  its  normal  allelomorph,  it  is  expected,  on  Boveri's 
view,  that  the  male  side  of  the  gynandromorph  should  show  this 
maternal  autosomal  character,  even  though  recessive.  But  on  the 
hypothesis  of  chromosomal  elimination,  both  sides  of  the  gynandro- 
morph should  show  the  same  autosomal  characters.  Conversely,  if 
the  cross  is  so  arranged  that  a  recessive  mutant  autosomal  gene  enters 
from  the  father's  side,  then,  on  Morgan's  earlier  view  of  polyspermic 
fertilization,  the  male  side  of  the  gynandromorph  should  show  this 
recessive  mutant  character;  but  on  the  elimination  hypothesis  both 
sides  should  show  the  same  (dominant)  autosomal  characters.  It 
may  now  be  shown  by  critical  examples  that  the  hypothesis  of  chromo- 
somal elimination  will  cover  nearly  all  of  the  cases  of  Drosophila,  and 
is  therefore  preferable  to  either  of  the  other  two,  even  although  in 
special  cases  either  of  these  two  other  ways  of  producing  gynan- 
dromorphs  may  be  reaUzed.  A  few  additional  cases  have  been  found 
that  call  for  still  other  interpretations. 

The  critical  cases  are  as  follows:  A  yellow  white  male  was  mated 
to  a  female  pure  for  the  recessive  autosomal  genes  for  peach  eye- 
color,  spineless  body,  kidney  eye-shape,  sooty  body-color,  and  rough 
eyes.  A  gynandromorph  was  found  (plate  1,  fig.  1)  that  was  male 
on  one  side,  as  shown  by  his  shorter  wing,  sex-comb  on  the  foreleg, 
and  the  shorter  bristles  characteristic  of  the  male  (the  body  was 
also  slightly  bent  to  the  smaller  male  side),  and  female  on  the  other 
side,  as  shown  by  the  converse  characters  to  those  just  given.  The 
gynandromorph  possesses  on  both  sides  all  of  the  characters  dominant 
to  the  five  recessive  autosomal  factors  that  came  in  with  the  sperma- 
tozoon. On  Boveri's  explanation,  the  male  side  should  have  a  yellow 
body-color  and  a  white  eye,  because  their  two  genes  are  carried  by 
the  maternal  nucleus,  while  the  female  side  should  show  the  normal 
characters  of  the  wild  fly,  as  is  the  case.  The  absence  of  yellow 
body-color  and  white  eyes  on  the  male  side  rules  out  his  explanation. 
On  Morgan's  hypothesis  of  polyspermy,  the  male  side  that  comes 
from  one  or  more  supernumerary  sperms  should  show  the  five  auto- 
somal recessive  characters  brought  in  by  each  sperm,  which  is  not 
the  case,  and  the  female  side  should  show  the  normal  characters,  as 
it  does.  The  absence  of  the  five  recessive  characters  on  the  male 
side  rules  out  this  explanation  also.  On  the  theory  of  chromosomal 
elimination  the  gynandromorph  started  as  an  ordinary  XX  female — 
one  X  carrying  the  genes  for  yellow  and  for  white,  the  other  carrying 
their  normal  allelomorphs,  viz,  genes  for  gray  and  for  red.  Either  of 
these  chromosomes  might  be  the  one  to  be  eliminated,  i.  e.,  at  some 
division  either  one  of  the  yellow  white  daughter  chromosomes  failed  to 
reach  one  of  the  daughter  cells,  or  one  of  the  gray  red  daughter  chromo- 
somes failed.     If  the  former,  the  male  side  should  get  only  the  gray 


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GYNANDROMORPHS  OF  DROSOPHILA 


THE    ORIGIN    OF   GYNANDROMORPHS.  1. 

red  chromosome,  and  show  the  corresponding  characters,  which  in  fact 
it  does.  If  the  other  chromosome  had  lost  one  of  its  halves  at  the 
critical  division,  the  male  side  should  be  yellow  white,  which  is  not  the 
case.  Evidently,  then,  it  must  have  been  a  yellow  white  daughter 
chromosome  that  was  lost  in  this  case.  In  regard  to  the  five  autosomal 
characters,  it  is  clear  that  since  both  male  and  female  sides  show  all  the 
dominant  characters,  both  sides  of  the  body  received  the  autosome  that 
bears  their  genes.  This  hypothesis  thus  covers  the  facts  in  the  case. 
Sections  of  the  abdomen  showed  abnormal  gonads  that  appeared  to 
be  testes. 

Another  gynandromorph  is  drawn  in  plate  1,  figure  2.  It,  too, 
came  from  this  same  cross  of  a  yellow  white  male  by  a  female  of  a 
race  with  the  same  five  recessive  characters.     It  is  not  a  bilateral 


Text-figure  2. 

gynandromorph,  but  more  nearly  an  anterior-posterior  combination. 
The  abdomen  is  male,  and  since  the  forelegs  bear  no  sex-combs,  some 
at  least  of  the  anterior  end  is  female.  One  wing  is  male;  at  least  it 
is  shorter  than  the  one  on  the  opposite  side,  which  is  presumably 
female.  As  in  the  last  case,  the  fly  shows  only  the  characteristics 
belonging  to  the  normal  allelomorphs  of  the  five  recessive  autosomal 
factors.    The  analysis  here  is  the  same  as  above. 

Another  gynandromorph,  drawn  in  text-figure  2,  arose  from  a  cross 
between  a  male  that  was  heterozygous  for  the  two  dominant  autosomal 
genes  for  star  eyes  and  for  dichaete  bristles  and  a  female  that  was  notch 


8  THE    ORIGIN   OF   GYNANDROMORPHS. 

(*  'short"  type) .  The  mother  had  one  sex  chromosome  with  the  dominant 
gene  for  notch  and  another  sex  chromosome  that  had  the  normal  allelo- 
morph of  notch  and  also  a  gene  for  eosin  eye-color.  The  gynandromorph 
was  male  on  one  side,  with  an  eosin  eye  (with  a  red  fleck  in  it),  a  sex- 
comb,  and  a  short  wing  on  that  side,  and  female  on  the  other  side  with  a 
red  eye,  no  sex-comb,  and  a  longer  wing.  The  genitalia  were  male. 
The  gynandromorph  arose  by  the  fertilization  of  an  egg  containing  the 
sex  chromosome  bearing  the  eosin  eye-color  (because  had  the  other 
maternal  X  chromosome  been  present  one  of  the  wings,  or  both,  would 
have  shown  the  notch  character).  In  this  case  it  was  the  X  chromo- 
some from  the  father  that  was  .eliminated,  since  the  male  side  shows 
the  eosin  eye-color  of  the  maternal  sex  chromosome.  Boveri's  ex- 
planation will  not  fit  this  case,  even  though  the  male  side  shows  a 
miaternal  character,  viz,  eosin  eye,  because  that  side  is  dichaete,  hence 
contains  dominant  factors  from  the  paternal  autosome.  Morgan's 
hypothesis  of  polyspermy  will  not  fit  this  case,  for  the  male  side  should 
have  red  instead  of  eosin  eye-color,  since  red  was  brought  in  by  the 
sperm.  On  the  hypothesis  of  elimination,  it  is  apparent  that  one  of 
the  daughter  halves  of  the  normal  X  chromosome  was  lost ;  the  cells  of 
both  sides  got  the  regular  autosomal  groups,  for  dichsete  came  from  the 
father.  The  father  was  heterogyzous  for  star,  and  it  must  have  been 
one  of  his  gametes  without  star,  but  with  dichsete,  that  fertilized  the  egg. 
Here  again  neither  of  the  earlier  explanations  fits  the  case,  but  the 
third  hypothesis  covers  it. 

Another  gynandromorph  was  described  in  ''Mosaics  and  Gynandro- 
morphs  in  Drosophila"  in  1914.  It  was  the  first  case  discovered  in 
which  the  presence  of  an  autosomal  factor  made  it  possible  to  decide 
which  of  the  three  explanations  was  the  correct  one.  A  yellow  white 
female  was  crossed  to  a  male  that  carried  a  recessive  autosomal  gene 
for  ebony  body-color.  The  gynandromorph  was  preponderantly  male 
on  one  side  and  female  on  the  other.  Both  eyes  were  red  and  the 
body-color  was  gray  (or  possibly  heterozygous  ebony)  on  both  sides. 
Here  Boveri's  explanation  fails,  because  the  male  side  should  have 
been  entirely  maternal,  therefore  yellow  and  white;  and  Morgan's 
earlier  explanation  fails,  because  the  male  side  was  not  ebony.  On 
the  elimination  hypothesis  a  maternal  yellow  white  daughter  chromo- 
some was  lost ;  hence  both  sides  had  red  eyes  and  not  yellow  body-color, 
and  both  sides  received  the  same  normal  autosomes.  This  cross, 
in  which  a  yellow  white  female  was  mated  to  an  ebony  male,  was 
carried  out  extensively  (January  to  May  1914)  and  6  more  gynandro- 
morphs  were  found.  However,  in  order  to  discriminate  between 
partial  fertilization  and  polyspermy  on  the  one  hand  and  elimination 
on  the  other  only  those  cases  are  diagnostic  in  which  the  male  parts 
come  from  the  father  and  show  at  the  same  time  autosomal  parts  from 
the  mother. 


THE    ORIGIN   OF   GYNANDROMORPHS. 


9 


Another  gynandromorph  (obtained  by  Sturtevant),  text-figure  3, 
came  from  a  mother  that  had  in  one  second  chromosome  the  genes 
for  C„i  and  for  curved,  and  in  the  other  the  genes  for  black  and  for 
vestigial.  She  may  have  had  a  third  chromosome  gene  for  crossing- 
over.  The  father  was  homozygous  for  black,  purple,  curved,  plexus, 
speck,  all  in  the  second  chromosome.  Brothers  and  sisters  were  as 
expected;  the  black  curved  crossing  over  was  28  per  cent.  The  fly 
was  black  and  showed  no  trace  of  purple,  vestigial,  curved,  plexus,  or 
speck.  It  was  male  on  the  left  side,  female  on  the  right,  except  for 
head  bristles.  The  genitalia  were  male.  The  fly  was  sterile.  Unless 
the  egg  were  a  double  cross-over  for  black  vestigial  curved,  which  is 
unlikely,  it  contained  a 
black  vestigial  bearing 
chromosome.  The  sperm 
contained  the  five  sec- 
ond-chromosome genes. 
Since  the  male  parts 
showed  none  of  these  sec- 
ond-chromosome char- 
acters, except  black, 
although  all  the  rest  ex- 
cept purple  might  have 
been  visible,  it  is  highly 
probable  that  the  male 
parts  contained  both  sec- 
ond-chromosomes. The 
result  shows  at  least  that 
the  theory  of  chromo- 
some elimination  is  a 
more  probable  explana- 
tion than  partial  ferti- 
lization or  multiple  ferti- 
lization, and  the  result 
would  be  conclusive  if 
the  possibility  of  double  crossing-over  were  rejected. 

Another  case  (found  by  Sturtevant,  4079  C,  Oct.  31,  1917)  occurred 
in  a  cross  betweem  a  male  with  a  normal  X  chromosome  and  pure  for 
the  second-chromosomal  genes  for  black,  purple,  and  curved,  and  a 
forked  female  that  was  heterozygous  for  the  second-chromosomal  genes 
for  black,  purple,  and  curved.  The  gynandromorph  (plate  1,  fig.  3) 
had  a  short  wing  on  the  left  side,  but  the  left  foreleg  was  not  male. 
The  abdomen  had  the  male  banding  and  genitalia  and  contained  two 
testes.  No  forked  bristles  were  found  in  any  part  of  the  body.  Elim- 
ination of  one  of  the  forked-bearing  maternal  X  chromosomes  left  the 
wild-type  X  chromosomes  to  determine  the  character  of  the  male  parts. 


Text-figure  3. 


10  THE    ORIGIN    OF    GYNANDROMORPHS. 

The  gynandromorph  must  have  received  the  normal  second  chromo- 
some from  its  mother  (since  normal  autosomal  characters  only  ap- 
peared) and  a  second  chromosome  from  its  father  with  the  three 
recessive  genes.  Since  neither  male  nor  female  parts  show  these 
recessive  genes,  two  second  chromosomes  must  have  been  present  in 
all  the  nuclei,  both  in  the  male  and  in  the  female  parts. 

FREQUENCY  OF  OCCURRENCE  OF  GYNANDROMORPHS. 

In  general,  we  have  no  record  of  the  frequency  of  the  occurrence 
of  gynandromorphs.  They  are  found  from  week  to  week,  their  number 
being  roughly  in  proportion  to  the  number  of  flies  passing  under 
observation,  and  also  in  proportion  to  the  care  with  which  the  flies 
are  scrutinized  in  detail.  On  four  occasions,  however,  the  frequency 
of  their  appearance  was  recorded. 

In  the  first  case  (in  1914)  a  cross,  involving  yellow  flies,  white-eyed 
and  eosin-eyed  flies,  and  wild-type  flies,  seemed  to  give  gynandromorphs 
more  often  than  usual.  It  is  to  be  noticed  that  the  striking  color 
differences  of  eye  and  body  in  this  combination  would,  as  a  rule,  make  it 
easy  to  detect  hybrid  gynandromorphs,  and  their  frequency  may  have 
been  due  to  this  fact.  In  all  32  gynandromorphs  were  found  in  a  total 
of  42,409  flies,  or  1  in  1,325. 

Duncan,  in  1915,  made  a  careful  examination  of  hybrid  flies  and 
found  3  gynandromorphs  in  a  total  of  16,637  flies,  or  1  in  5,500.  All 
flies  were  so  thoroughly  scrutinized  that  probably  most  of  the  gynan- 
dromorphs that  occurred  were  found. 

The  third  set  of  observations  was  made  on  material  that  was  chosen 
because,  in  addition  to  sex-linked  factors,  autosomal  genes  were  present, 
which  should  give  an  answer  to  the  three  contrasted  hypotheses  de- 
scribed in  the  preceding  pages.  In  all,  2  gynandromorphs  were  found 
in  a  total  of  4,979  flies. 

A  fourth  record  made  by  Sturtevant  also  involved  autosomal  as 
well  as  sex-linked  characters.  Forked  females  were  mated  to  males 
with  normal  bristles.  The  female  was  heterozygous  for  the  second- 
chromosome  genes,  black,  purple,  curved;  the  male  homozygous  for 
the  same  genes;  3  gynandromorphs  were  found  in  about  24,000 
offspring. 

Taking  all  these  results  together,  the  observed  ratio  is  1  gynandro- 
morph in  2,200  flies. 

Whenever  the  chromosomal  elimination  occurs  at  an  early  stage  in 
development,  or  when  the  color  or  structural  difference  involved  is 
striking,  the  gynandromorph  is  more  likely  to  be  found  than  when  the 
contrary  conditions  are  present.  If  elimination  occurs  late  in  develop- 
ment the  region  affected  may  be  so  small  as  to  escape  detection. 
It  seems  probable,  therefore,  that  such  irregularities  may  be  more 
frequent  than  the  figures  given  above  indicate. 


THE    ORIGIN    OF   GYNANDROMORPHS.  11 

It  is  a  curious  fact  that  practically  all  of  the  mosaics  of  Drosophila 
involve  the  sex  chromosomes.  It  is  true  that  the  differences  in  the 
sexes  are  so  marked  that  individuals  partly  male,  partly  female,  could 
easily  be  detected  on  this  basis  alone.  On  the  other  hand,  the  mutant 
characters  that  are  sex-linked  are  not  more  striking  than  are  those  of 
autosomal  mutants.  The  almost  complete  absence  of  the  latter  kind 
of  mosaics  in  our  cultures  shows  very  positively  that  elimination  is  very 
infrequent  in  these  chromosomes,  or,  if  it  occurs,  that  an  individual  or 
part  with  only  one  autosome  is  less  likely  to  survive  than  an  individual 
with  one  X  chromosome.  Until  this  question  is  settled  it  can  not 
safely  be  concluded  that  the  sex  chromosomes  suffer  elimination  more 
than  do  the  autosomes.  The  fact  that  autosomal  non-disjunction  has 
not  yet  been  observed  in  Drosophila,  though  looked  for,  lends  support 
to  the  view  that  variations  in  autosomal  number  are  either  rare  or  are 
fatal. 

RELATIVE  FREQUENCY  OF  ELIMINATION  OF  THE  MATERNAL 
AND  PATERNAL  SEX  CHROMOSOME. 

It  might  have  been  supposed  a  priori  that  delay  in  the  unraveling  of 
the  chromosomes  of  the  sperm  might  be  the  most  frequent  cause  of 
the  elimination  of  chromosomes.  As  a  matter  of  fact,  the  evidence 
shows  clearly  that  the  maternal  X  is  as  likely  to  be  eliminated  as  the 
paternal.  For  example,  we  find  on  looking  through  our  records  that  in 
15  cases  the  maternal  X  chromosome  and  in  15  cases  the  paternal 
chromosome  must  have  been  the  one  eliminated.  There  were  16  cases 
in  which  from  the  nature  of  the  cross  or  of  the  result  it  could  not  be 
determined  which  one  was  eliminated.  In  the  above  estimation  we 
also  have  left  out  of  account  all  cases  that  were  entirely  male,  or  for 
which  special  explanations  are  called  for.  There  can  then  be  no  doubt 
but  that  eUmination  is  somehow  connected  with  the  nature  of  the  X 
chromosomes  themselves,  such  as  slowness  in  dividing  or  in  reaching  the 
poles  of  the  spindle,  and  that  elimination  is  not  due  to  delay  in  the 
development  of  either  pronucleus. 

An  examination  of  the  gonads  in  Drosophila  gynandromorphs  has 
shown  in  every  case  that  the  two  gonads  are  the  same,  i.  e.,  both  are 
ovaries  or  both  are  testes.  Even  in  bilateral  types  the  two  gonads  are 
alike.  Duncan  found  this  true  for  the  few  cases  that  he  sectioned. 
This  number  was,  however,  insufficient  to  establish  the  rule,  but  we  can 
now  add  about  20  other  cases  to  the  list.  There  can  remain  no  doubt 
that  the  gonads  are  alike,  regardless  of  the  way  in  which  the  male  and 
female  parts  are  distributed  on  the  surface.  The  results  are  in  accord 
with  the  early  formation  of  the  germ-cells  in  Diptera  and  probably  mc^n 
that  both  gonads  are  derived  from  one  and  the  same  cleavage  nucleus. 


12  THE    ORIGIN    OF    GYNANDROMORPHS. 

DISTRIBUTION  OF  SEGMENTATION  NUCLEI  AS  DEDUCED  FROM  DIS- 
TRIBUTION  OF  THE  CHARACTERS  OF  GYNANDROMORPHS. 

If  the  first  division  of  the  segmentation  nucleus  corresponds  with 
the  right  and  left  sides  of  the  embryo,  and  if  chromosomal  eUmina- 
tion  is  more  common  at  this  time  or  more  easily  detected,  we  should 
expect  most  gynandromorphs  to  be  roughly  bilateral.  We  have  found 
that  this  is  the  most  frequent  type.  If  the  first  division  were  in  the 
antero-posterior  direction  and  elimination  were  frequent  at  this  time, 
we  should  expect  to  find  some  gynandromorphs  with  the  anterior  end  of 
one  sex  and  the  posterior  end  of  the  other  sex.  This  type  also  is  fairly 
frequent. 

If  the  first  division  were  dorso-ventral  we  might  expect  correspond- 
ing gynandromorphs,  but,  although  more  difficult  to  detect,  they 
appear  almost  never  to  be  of  this  kind. 

If  the  second  division  were  a  time  of  elimination  we  would  expect 
quadrants  instead  of  halves.     Such  cases  are  known. 

The  striking  fact  about  the  gynandromorphs  is  that  large  regions 
of  the  body  are  involved.  Granting  that  later  differences  would  be 
less  easily  detected,  in  certain  organs  at  least,  the  results  are  so  em- 
phatically in  favor  of  large  parts  of  the  body  being  involved  that  we 
think  it  highly  probable  that  the  elimination  is  most  frequent  in  the 
first  division. 

The  difficulty  of  reaching  a  decision  is  greatly  increased  when  it  is 
recalled  that  from  the  ventral  plate  of  the  embryo  the  serosa  is  formed 
by  a  folding  upward  of  the  sides  of  the  plate.  How  much  of  the  ventral 
ectoderm  is  carried  in  this  way  to  the  dorsal  surface  is  not  known. 
Should  it  replace  the  dorsal  covering  derived  from  the  segmentation 
nuclei  (that  goes  then  into  the  serosa  which  is  later  thrown  off),  the 
results  for  ectodermal  organs  are  restricted  to  the  regions  on  each  side 
of  the  ventral  plate.  The  mesoderm  also  grows  from  the  ventral  to 
the  dorsal  surface,  and  presumably  mesodermal  dorsal  structures  have 
come  from  ventral  material. 

A  further  complication  arises  in  connection  with  the  imaginal  plates 
out  of  which  many  adult  organs  are  produced.  Unless  the  exact  origin 
of  their  cells  is  known,  it  is  not  possible  to  safely  conclude  at  what  time 
the  early  elimination  takes  place. 

STARTING  AS  A  MALE  VERSUS  STARTING  AS  A  FEMALE. 

The  evidence  recorded  in  the  preceding  pages  is  analyzed  on  the 
basis  that  the  gynandromorph  starts  as  an  XX  individual,  or  female, 
and  that  the  male  parts  arise  by  the  elimination  of  an  X  from  one 
of  the  cells.  The  evidence  from  hybrid  combinations  shows  very 
clearly  that  practically  all  of  our  gynandromorphs  have  started  as 
XX  individuals,  as  19  are  more  female,  14  nearly  equal,  6  more  male. 


THE    ORIGIN    OF   GYNANDROMORPHS.  13 

There  are,  however,  other  theoretical  possibiHties  that  should  be 
noticed,  for  it  is  possible  that  gynandromorphs  may  sometimes  arise 
in  other  ways.  In  fact,  one  or  two  of  those  we  describe  may  he  ex- 
plained in  the  following  way :  An  X  egg  fertilized  by  a  Y  sperm  (a  regular 
male),  might  later  become  partly  female,  i.  e.,  gynandromon)h,  through 
somatic  non-disjunction,  both  daughter  X's  remaining  in  the  same  cell 
at  some  early  embryonic  division.  Parts  descended  from  the  XXY 
cell  are  female;  the  other  (Y)  cell  would  presumably  die.  If  such  a 
process  occurred  at  the  first  division  and  all  of  the  yolk  was  later  occu- 
pied by  the  viable  XXY  cells,  the  embryo  would  become  entirely 
female,  although  containing  only  sex-linked  genes  from  the  mother, 
and  might  be  mistaken  for  a  case  of  'primary  non-disjunction.' 

A  non-disjunctionally  produced  egg  containing  a  Y  chromosome 
or  an  egg  without  a  sex  chromosome  fertilized  by  an  X  sperm  might 
also,  starting  as  a  male,  produce  a  purely  paternal  female  or  female 
parts  (mosaic)  through  somatic  non-disjunction.  If  non-disjunction 
occurred  at  a  late  division  a  proportionately  smaller  part  of  female 
tissue  would  be  formed  and  the  regular  male  cells  formed  earlier  would 
give  male  parts — i.  e.,  the  individual  might  be  more  male  than  female. 

There  are  no  cases  where  these  explanations  only  will  apply,  but  a 
few  cases  accounted  for  by  chromosome  elimination  may  be  also 
explained  in  one  or  the  other  of  these  ways,  viz,  that  the  gj-^nandro- 
morph  started  as  a  male. 

CYTOLOGICAL  EVIDENCE  OF  CHROMOSOMAL  ELIMINATION. 

The  most  important  case  of  chromosomal  elimination  involving 
one  of  the  sex  chromosomes,  and  therefore  most  like  the  case  of 
gynandromorphism  in  Drosophila,  has  been  described  in  Ascaris 
(Rhabditis)  nigrovenosus  by  Boveri  and  by  Schleip.  In  this  nematode 
there  is  a  hermaphroditic  generation  that  lives  in  the  lungs  of  the 
frog.  Eggs  and  sperm  are  produced  at  the  same  time  in  the  her- 
maphroditic gonad.  The  full  number  of  chromosomes  is  the  same 
in  the  earlj'-  oogonia  and  spermatogonia.  This  number  is  reduced  to 
half  in  the  egg  and  also  in  the  sperm  at  the  reduction  division,  but 
while  all  the  eggs  are  alike,  there  are  two  kinds  of  spermatozoa,  one 
containing  one  less  chromosome  than  the  other.  This  loss  of  one 
of  the  chromosomes  in  one-half  of  the  sperm-cells  is  apparently  brought 
about  as  a  regular  process  by  the  failure  at  reduction  of  one  member  of 
the  paired  sex  chromosomes  to  reach  the  pole.  It  is  caught  at  the 
division  plane  or  else  remains  near  that  plane  and  disappears.  This 
process  differs  however,  from  what  we  suppose  to  occur  in  eliminating 
a  sex  chromosome  in  Drosophila  when  a  gynandromorph  is  produced 
in  that  an  undi\'ided  X  is  lost.  Whether  in  Ascaris  this  process  occurs 
in  all  the  cells  at  a  given  division  or  is  somewhat  irregular  is  not  certain, 
and  can  only  be  determined  by  a  fuller  knowledge  of  the  ratio  of  males 


14  THE    ORIGIN   OF   GYNANDROMORPHS. 

to  females  that  result.  Boveri  thought,  from  the  evidence  obtained, 
that  the  loss  of  one  chromosome  at  this  time  is  a  constant  phenomenon. 
If  so,  it  differs  in  this  regard  from  the  rare  occurrence  of  eUmination 
in  Drosophila. 

In  the  group  of  aphids  and  phylloxerans  a  process  occurs  that  has  at 
least  a  certain  analogy  to  elimination.  When  the  male-producing  egg, 
which  is  smaller  (in  the  latter  group)  than  the  female-producing 
egg,  throws  off  its  single  polar  body,  one  sex  chromosome  is  eliminated 
from  the  egg,  although  the  autosomes  divide  equationally  at  this 
time.  This  elimination  is  not  due  to  loss  of  a  daughter  chromosome, 
because  it  is  preceded  by  a  sort  of  synaptic  union  and  disjunction  of  the 
chromosome  in  question.  Here  the  lagging  of  one  whole  chromosome 
in  the  middle  part  of  the  spindle,  and  its  failure  to  reach  the  outer 
pole  in  time  to  become  incorporated  in  the  nucleus  of  the  polar  body, 
furnishes  a  certain  resemblance,  at  least,  to  the  elimination  process. 

In  one  species,  P.  fallax,  there  are  four  sex  chromosomes,  two  of 
which  are  eliminated  from  the  male-producing  egg,  as  described  above. 
There  remain,  then,  two  sex  chromosomes  in  the  male.  When  the 
sperms  are  produced  these  two  do  not  act  as  mates  when  the  other 
chromosomes  (autosomes)  pair  and  segregate,  but  both  pass  together 
to  one  pole.  The  daughter  cells  that  get  them  become  the  functional 
female-producing  spermatozoa;  the  other  cell  that  lacks  them  de- 
generates. Here,  then,  although  two  sex  chromosomes  are  present, 
they  both  pass  to  one  pole.  This  behavior  is  quite  unlike  the  results 
produced  by  chromosomal  elimination. 

In  one  of  the  aphids  Morgan  found  a  cyst  in  which,  owing  apparently 
to  the  failure  of  the  autosomes  to  pair  before  segregation,  an  irregular 
distribution  of  the  chromosomes  took  place,  including  an  erratic  dis- 
tribution, somewhat  imperfect,  it  is  true,  of  the  sex  chromosomes 
also.  This  unusual  and  irregular  occurrence  might  lead  to  compUca- 
tion  in  the  distribution  of  the  sex  chromosomes  in  the  next  generation, 
if  such  sperm  were  to  become  functional,  and  furnish  a  parallel  case 
to  the  phenomenon  of  primary  non-disjunction  that  Bridges  has 
described  in  Drosophila. 

In  Drosophila  there  takes  place  on  rare  occasions  an  erratic  distribu- 
tion of  the  sex  chromosomes,  either  in  the  male  or  in  the  female,  that 
has  been  called  primary  non-disjunction.  Occasionally,  both  sex  chromo- 
somes are  eliminated  in  the  polar  body,  leaving  in  the  egg  the  haploid 
number  of  chromosomes,  but  not  a  sex  chromosome.  If  such  an  egg  is 
fertilized  by  a  female-producing  sperm  containing  one  X  chromosome, 
an  XO  male  results.  The  male,  lacking  the  characteristic  Y  chromo- 
some of  the  normal  male,  nevertheless  resembles  a  normal  male  in  all 
respects,  except  that  he  is  sterile.  Conversely,  in  other  cases,  both  X 
chromosomes  may  remain  in  the  egg.  Such  an  egg  does  not  develop 
if  it  is  fertilizied  by  a  female-producing  sperm  giving  it  three  X's,  but 


THE    ORIGIN   OF   GYNANDROMORPHS.  15 

if  such  an  egg  is  fertilized  by  a  male-producing  Y-bearing  sperm,  it 
produces  a  female  XXY,  that  is  like  a  normal  female  in  its  somatic 
characters;  but  such  a  female,  owing  to  the  presence  of  three  sex 
chromosomes  (XXY),  gives  rise  to  the  phenomenon  of  secondary' 
non-disjunction  to  be  described  presently. 

Similarly  in  the  male,  primary  non-disjunction  may  take  place  in 
the  formation  of  the  spermatozoon.  If  at  the  reduction  division  the 
X  and  Y  chromosomes,  that  normally  pass  to  opposite  poles,  should 
pass  to  one  pole,  a  spermatozoon  would  result  from  one  of  the  daughter 
cells  that  contains  both  an  X  and  a  Y,  and  such  a  sperm  fertilizing 
an  X-bearing  egg  would  give  rise  to  an  XXY  female  that  would 
exhibit  secondary  non-disjunction.  The  other  daughter  cell  without 
X  or  Y  also  produces  a  functional  sperm.  In  these  cases  of  primary 
non-disjunction  an  irregular  distribution  of  the  sex  chromosomes  leads 
to  unusual  tj-pes  of  sex-linked  inheritance,  but  not  to  gynandro- 
morphism  or  to  mosaics. 

In  secondary  non-disjunction,  owing  to  the  presence  of  three  sex 
chromosomes,  any  two  of  which  may  form  a  pair,  there  is  left  one 
chromosome  without  a  mate.  Genetic  analysis  shows  that  the  un- 
paired chromosomes,  in  some  cases  one  of  the  X's,  in  others  the  Y, 
may  either  pass  out  of  the  egg  at  maturation  or  remain  in  the  egg. 
Aside  from  this  irregularity  there  is  not  much  in  the  process  that  is 
akin  to  the  kind  of  chromosomal  elimination  postulated  for  gynandro- 
morphs,  since  the  processes  underlying  the  two  phenomena  are  prob- 
ably quite  different.  These  cases  furnish  exceptions  in  regard  to 
genetic  behavior  and  furnish  important  evidence  bearing  on  the  deter- 
mination of  sex,  but  do  not  lead  to  the  kinds  of  effects  seen  in  the  pro- 
duction of  gynandromorphs,  except  when  the  non-disjunction  occurs 
at  a  cleavage  stage,  as  already  explained. 

As  stated,  Boveri  based  his  hypothesis  of  gynandromorph  produc- 
tion on  an  earlier  observation  that  he  had  made  with  the  sea-urchin 
eggs.  He  found  that  occasionally  the  egg-nucleus  began  to  divide 
before  the  sperm-nucleus  had  fused  with  it.  In  consequence,  the 
sperm-nucleus  fertilized,  as  it  were,  only  one-half  of  the  egg;  i.  e., 
it  approached  one  of  the  two  daughter  nuclei,  and  later  became 
incorporated  with  that  one.  In  consequence,  all  the  nuclei  descending 
from  this  fusion  had  the  diploid  number  of  chromosomes,  while  the 
nuclei  descending  from  the  single  daughter  egg-nucleus  had  only  the 
haploid  number.  In  the  sea-urchin  it  has  not  been  found  possible  to 
raise  plutei  fo  maturity;  hence  the  effect  of  this  partial  fertilization  on 
sex  could  not  be  determined.  Boveri's  application  of  this  evidence  to 
gynandromorphs  of  the  bee  was  purely  theoretical,  since  at  that  time 
the  genetic  evidence,  that  has  since  become  available,  did  not  exist. 

At  about  the  same  time  Herbst  carried  out  some  experiments  with 
sea-urchin  eggs  that  enabled  him  to  produce  a  large  number  of  em- 


16  THE   ORIGIN   OF   GYNANDROMORPHS. 

bryos  in  which  a  process  similar  to  that  just  described  took  place. 
The  unfertilized  eggs  were  stimulated  to  parthenogenetic  develop- 
ment by  placing  them  in  sea-water  containing  a  little  valerianic  acid. 
After  a  few  minutes  the  eggs  were  returned  to  sea-water  and  sperm 
added.  The  sperm-nucleus  did  not  penetrate  in  many  cases  until 
the  egg  nucleus  had  begun  to  divide  and  then,  as  in  Boveri's  case,  it 
often  united  with  one  of  the  daughter  nuclei.  In  neither  of  the  cases 
is  there  any  elimination  of  single  chromosomes,  but  in  a  more  general 
sense  the  earlier  group  of  paternal  chromosomes  was  dislocated  in 
that  it  failed  to  reach  its  normal  destination. 

The  extremely  important  experiments  that  Baltzer  made  with  sea- 
urchin  eggs  resulted  in  demonstrable  cases  of  elimination,  but  here  of 
whole  undivided  chromosomes.  For  instance,  when  the  eggs  of 
Strongylocentrotus  are  fertilized  with  the  sperm  of  Sphoer echinus,  it 
is  found  at  the  first  division  of  the  egg  that  while  some  of  the  chromo- 
somes divide  and  the  halves  move  to  opposite  poles,  other  chromo- 
somes remain  in  place,  or  become  scattered  irregularly  between  the 
two  poles  of  the  spindle.  They  appear  later  as  irregular  granules  and 
show  signs  of  degeneration,  and  although  remnants  of  them  may 
persist  for  a  while,  they  take  no  further  part  in  the  development. 
The  maternal  egg-nucleus  contained  in  this  case  18  chromosomes 
and  likewise  the  paternal  sperm-nucleus.  Hence,  after  union  and 
division,  36  chromosomes  should  go  to  each  pole  of  the  segmentation 
spindle  if  all  divided.  Baltzer  found,  however,  only  21  chromosomes 
at  each  pole,  which  means  that  15  chromosomes  have  failed  to  behave 
normally,  and  it  is  probable  that  these  are  derived  from  the  paternal 
nucleus.  Three  chromosomes  only  of  the  latter,  on  this  interpreta- 
tion, take  part  in  the  division.  In  consequence,  the  nuclei  of  the 
embrj'o  contain  almost  exclusively  maternal  chromosomes,  and  it 
is  significant  that  the  larvae  are  largely  or  entirely  maternal  in  char- 
acter. It  is  true  that  we  have  no  evidence  to  show  at  present  that 
the  larvae  of  these  sea-urchins  differ  in  only  one  or  more  Mendelian 
factors.  It  would  be  very  surprising  if  such  were  the  case,  yet  the 
results  show  at  least  so  great  a  preponderance  of  maternal  characters 
that  we  must  infer  that  the  three  surviving  paternal  chromosomes 
produce  no  marked  difference. 

The  reciprocal  cross  gave  a  different  result.  When  the  eggs  of 
Sphcerechinus  are  fertilized  by  the  sperm  of  Strongylocentrotus,  di\asion 
of  all  of  the  chromosomes  takes  place  normally  and  36  are  found  at 
each  pole.  The  pluteus  that  develops  shows  peculiarities  of  both 
paternal  and  maternal  types.  The  difference  between  the  two  crosses 
is  probably  due  to  the  observed  differences  in  the  behavior  of  the 
chromosomes.  In  the  first  case,  the  lagging  and  subsequent  degenera- 
tion of  certain  chromosomes  may  be  spoken  of  as  a  sort  of  elimination, 
although  the  causes  that  bring  it  about  must  be  supposed  to  be  of  a 


Raleigh       ^ 

THE    ORIGIN   OF*^?;fejmBr)MORPHS.  17 

different  kind  from  those  involved  in  Drosophila  when  a  half  of  a  single 
chromosome  fails  to  reach  its  normal  destination,  * 

EARLIER  HYPOTHESES  TO  EXPLAIN  GYNANDROMORPHS. 

Dalla  Torre  and  Friese  (1897)  and  Mehling  (1915)  have  reviewed 
the  earlier  attempts  to  account  for  gynandromorphs.  D()nhofT  (1860) 
suggested  that  gynandromorph  bees  arose  from  eggs  with  two  yolks, 
one  of  which  was  fertilized,  the  other  not;  one  began  to  form  a  worker, 
the  other  a  drone,  both  fusing  into  one  individual  later.  A  second 
interpretation  based  on  Dzierzon's  theory  was  also  suggested,  viz,  that 
the  egg  contains  the  male  potentiality,  the  sperm  the  female  poten- 
tiality. In  fertilized  eggs  the  latter  influence  usually  predominates. 
In  the  gynandromorph,  one  of  these  influences  predominates  in  one 
region,  the  other  in  other  regions.  In  1861,  Wittenhagen  suggested 
that  a  queen  that  produces  gynandromorphs  has  reached  a  higher 
stage  of  fertility  which  causes  male  parts  to  arise  even  after  fertiliza- 
tion. Menzel  (1862)  made  several  guesses,  such  as  that  delayed  fer- 
tilization of  the  egg  leads  to  irregular  distribution  of  the  mass  of  the 
sperm  material  with  consequent  disturbance  in  the  development. 
Later  (1864)  he  suggested  that  abnormal  organization  of  the  oviducts, 
leading  to  delay  in  passing  of  the  egg,  interferes  with  the  sperm,  so 
that  the  egg  no  longer  has  the  possibility  of  producing  a  complete 
female,  except  in  certain  regions  of  the  body. 

Von  Siebold  (1864)  thought  that  insufficient  fertihzation  is  re- 
sponsible for  the  appearance  of  gynandromorphs.  He  assumed  that 
a  definite  number  of  spermatozoa  are  necessary  to  produce  a  female. 
When  from  any  cause  an  insufficient  number  of  sperms  is  present,  the 
egg  can  not  develop  a  female,  or  a  male,  but  an  intermediate  type. 

According  to  Cockayne  (1915,  p.  117),  Scopoli  (1777)  suggested 
that  a  gynandromorph  of  Phalcena  pini  might  have  arisen  through  the 
fusion  of  two  pupae  lying  in  one  cocoon.  Donhoff's  suggestion  (as 
above)  of  two  yolks  in  one  shell  that  fused  is  a  somewhat  similar  view, 
and  Wheeler  in  1910  made  a  like  suggestion,  viz,  that  two  eggs  (fer- 
tilized?) fused  at  a  very  early  stage,  one  a  male-producing,  the  other  a 
female-producing.  Such  a  process  will  not  apply,  however,  to  most 
of  the  cases  in  Drosophila,  because  the  evidence  shows  that  the  eggs 
are  normally  not  of  two  kinds.  The  male  alone  produces  two  kinds  of 
gametes.  The  sex-hnked  characters  in  hybrid  gynandromorphs  show 
very  clearly  that  the  results  are  not  due  to  the  fusion  of  two  eggs, 
but  to  a  different  sort  of  process.  In  the  bee  also  it  appears  that  there 
is  only  one  kind  of  egg,  and  that  the  female  sex  is  determined  by  the 
fertilization  of  the  egg;  the  male  comes  from  the  unfertilized  egg. 

On  the  other  hand,  there  are  several  cases  in  Drosophila  which  can 
not  be  explained  by  simple  chromosomal  elimination,  but  which  can 
be  explained  on  the  assumption  that  the  egg  had  two  nuclei.     Here 


18  THE    ORIGIN   OF   GYNANDROMORPHS. 

the  appeal  is  made  to  a  binucleated  egg  in  order  to  account  for  the 
distribution  of  the*  sex-linked  characters,  but  only  indirectly  for  the 
sex  differences  in  the  gynandromorph.  The  different  sexes  in  the 
two  parts  are  due  to  fertiUzation  of  the  two  nuclei  by  male  and  female 
producing  sperm  respectively.  The  presence  of  two  nuclei  in  these 
eggs  is  easily  explained  as  due  to  the  fusion  of  two  oogonial  cells  or 
else  by  an  oogonial  nuclear  division  without  cytoplasmic  division. 
The  conditions  existing  at  the  completion  of  the  last  oogonial  division 
are  particularly  favorable  for  such  a  union,  for  at  this  stage  from  a 
collection  of  cells  (presumably  all  aUke)  the  most  favorably  situated 
turns  into  the  egg  and  the  others  into  nurse-cells  very  intimately  con- 
nected with  the  egg-cell.  This  view,  while  similar  to  Wheeler's,  puts 
a  different  emphasis  on  the  facts,  for  here  the  presence  in  the  eggs  of 
two  nuclei  does  not  directly  account  for  the  different  sex  of  the  parts 
of  the  gynandromorph  (for  this  difference  is  due  to  the  two  kinds  of 
sperm  that  have  entered),  but  explains  the  distribution  of  the  sex- 
linked  characters  in  the  hybrid  gynandromorphs.  On  the  other 
hand,  Wheeler's  idea  is  that  two  eggs  in  themselves  determined  as 
male  and  female  fuse  bodily,  i.  e.,  side  by  side,  to  give  rise  to  male 
and  female  parts  respectively.  His  view  would  be  more  nearly  reahzed 
in  the  case  of  moths  where  the  female  is  the  heterozygous  sex,  and 
consequently  a  binucleated  condition  can  be  utilized  directly  to  ex- 
plain not  only  the  difference  of  sex  in  the  gynandromorph  (one  nucleus 
retaining  a  Z  and  the  other  a  W  chromosome),  but  also  the  autosomal 
mosaics,  as  in  the  cases  described  by  Toyama. 

Arnold  Lang  suggested  another  possibility  in  1912,  viz,  that  an  egg 
that  had  developed  parthenogenetically  to  the  stage  when  the  first 
two  nuclei  were  formed  might  be  fertilized  by  a  female  and  a  male 
producing  sperm,  each  sperm  uniting  with  one  or  the  other  of  the  two 
egg-nuclei.  As  a  result  one  half  should  be  male,  the  other  half  female. 
The  hypothesis  will  not  apply,  however,  to  the  bee — the  forms  whose 
parthenogenetic  process  of  development  would  seem  to  best  fit  such 
a  view — because  only  one  kind  of  sperm  is  supposed  to  be  produced. 
Double  nuclei  should  produce  female  parts.  The  explanation  will 
also  obviously  not  apply  to  such  cases  in  Drosophila  as  those  in  which 
the  male  half  shows  maternal  recessive  factors. 

De  Meijere  (1910-11)  has  offered  certain  suggestions  concerning 
the  origin  of  gynandromorphs.  He  starts  from  the  old  idea  that  each 
individual,  male  or  female,  contains  within  itself  the  characters  of 
the  opposite  sex.  He  thinks  that  this  holds  for  the  gametes  as  well 
as  for  the  somatic  cells.  Darwin  held  a  similar  view  and  thought 
that  this  was  true  not  only  for  the  primary  sex-cells  (sperm  and  eggs) 
but  for  the  secondary  sexual  characters  as  well.  To-day,  however,  it 
is  clear  that  such  a  statement,  at  least  in  regard  to  the  estabhshed  cases 
of  sex  determination  by  means  of  sex  factors,  calls  for  a  more  definite 


THE    ORIGIN    OF    GYNANDROMORPHS. 


19 


pronouncement  as  to  the  sense  in  which  the  phrase  is  employed; 
otherwise  it  is  Httle  more  than  a  play  on  words.  For  instance,  when 
one  X  chromosome  is  present  the  individual  is  a  male,  which  means 
that  one  X  plus  all  the  rest  of  the  cell  makes  a  male,  and  when  two 
X's  are  present,  these  two  plus  all  the  rest  of  the  cell  make  a  female. 
In  what  sense  can  such  a  statement  be  twisted  to  mean  that  each  such 
combination  contains  in  a  latent  condition  the  opposite  condition? 
Compare  the  facts  with  a  similar  chemical  situation  and  the  absurdity 
of  the  inclusion  hypothesis  is  evident.  Maltose  has  the  formula 
C12H22O11  and  glucose  the  formula  C6H12O6.  One  is  twice  the  other 
minus  one  H2O.  To  state  that  maltose  contains  glucose  latent  or  that 
glucose  contains  maltose  latent  is  obviously  absurd,  yet  this  does  not 
differ  much  from  the  view  that  each  sex  contains  the  opposite  one  in 
latent  form. 

De  Meijere  thinks  that  gynandromorphs  can  be  explained  in  "that 
the  activation  of  the  opposite  sex  (opposite  to  the  one  already  under 
way)  has  started  in,  relatively  later,  after  all  the  parts  have  taken 
on  their  definite  positions ;  many  of  the  parts  have  gone  too  far  in  the 
first  direction,  i.  e.,  they  are  too  old,  but  those  that  have  not  may  be 
turned  aside  and  produce  the  oppo-  ^  ^ 

site  results."^  This  view  is  offered 
to  account  for  mosaics  of  sex  char- 
acter. The  bilateral  gynandro- 
morph,  he  supposes,  owes  its  origin 
to  the  above  changes  having  taken 
place  very  early,  even  at  the  first 
division.  De  Meijere  thinks  ap- 
parently of  effects  being  produced 

by  external  factors  of  some  unknown  kind  rather  than  internal  ones 
connected  with  a  sex  mechanism.  His  idea  is  too  vague  to  be  of  use 
and  too  remote  from  present-day  knowledge  about  sex  determination 
to  call  for  extended  criticism. 

.  Arnold  Lang,  accepting  the  same  general  conception  of  sex  and 
expressing  what  he  beheved  to  be  the  real  relations  by  means  of  the 
formulae  that  Goldschmidt  had  advocated,  offered  another  possible 
interpretation  of  gynandromorphs  that  is  superficially  exactly  like 
the  theory  of  chromosomal  ehmination  which  the  results  in  Drosophila 
show  to  hold  for  this  insect.  In  fact,  Lang's  view,  if  divested  of  the 
unnecessary  encumbrance  of  De  Meijere's  conception  and  of  Gold- 
schmidt's  formulae,  is  then  identical  with  the  theory  of  chromosomal 
elimination.  For  example,  Lang  represents  the  fertilized  egg  (one 
that  will  give  rise  to  a  female)  by  the  scheme  shown  in  text-figure  4. 
The  primary  sex  characters  for  the  male  are  M  carried  by  a  pair  of 


TEXT-FIOURE8    4    AND    5. 


*  See  Goldschmidt'a  view  in  respect  to  the  rate  of  development  of  male  and  female  orgaoa  in 
the  intersexes  of  the  gipsy  moth. 


20  THE   ORIGIN    OF   GYNANDROMORPHS. 

chromosomes  that  also  carries  the  factors  for  the  secondary  sexual  char- 
acter A.  The  primary  sex  character  of  the  female  is  represented  by  F, 
carried  by  a  second  pair  of  chromosomes,  and  the  secondary  sexual 
character  by  G,  both  as  before,  carried  in  the  same  chromosome.  In 
other  words,  the  two  pairs  of  sex  chromosomes  are  (FG)  (FG)  and  (MA) 
(MA)  for  the  female,  and,  for  the  male,  (FG)  (fg)  and  (MA)  (MA). 

Lang  suggests  that  a  loss  by  mutation  takes  place  in  females  (as 
above)  in  the  sense  that  one  FG  disappears  and  may  now  be  repre- 
sented by  (fg).  The  resulting  division  is  shown  in  text-figure  5.  The 
mutation  causes  the  sex-balance  in  the  cell  on  the  right  side  to  turn 
into  a  male,  while  that  of  the  left  remains  a  female.  Lang  appears  to 
mean  that  the  "mutation  by  loss "  is  the  loss  of  a  daughter  chromosome. 

If  we  ignore  the  special  interpretation  of  sex  employed  by  Lang  and 
borne  out  by  his  formulae,  his  view  has  several  points  in  common  with 
the  hypothesis  of  chromosomal  elimination.  It  should  be  noted, 
however,  that  there  are  also  differences  in  the  apphcation  of  Lang's 
and  the  present  interpretation,  when  the  question  of  the  sex-linked 
factors  is  involved,  because  the  two  X  chromosomes  represented  by 
Lang  by  FG,  FG  carry  many  other  genes,  besides  those  for  sex,  even 
some  for  secondary  sexual  characters.  Which  of  these  comes  to 
expression  in  the  hybrid  gynandromorph  depend  on  which  FG  is  elim- 
inated and  not  on  the  resulting  change  in  balance  (epigenetic  effects) 
between  the  FG's  and  the  MA's.  Furthermore,  Lang's  scheme  in- 
volves the  relation  between  two  pairs  of  chromosomes  (four  in  all) 
while  in  the  actual  case  of  Drosophila  only  one  pair  is  needed  to  account 
for  all  the  facts. 

Cockayne,  in  1915,  announced  independently  the  same  view  of 
elimination  that  Morgan  had  published  the  year  before.  He  had 
found  several  halved  gynandromorphs,  all  of  which  showed  the  specific 
characters  of  both  parents  on  both  sides.  Both  parental  nuclei  must 
therefore  have  contributed  to  both  sides.  He  points  out  that  since 
the  division  into  male  and  female  parts  sometimes  coincides  with 
other  characters  the  latter  must  be  carried  by  the  sex  chromosomes. 

Doncaster,  in  1914,  described  binucleated  eggs  in  Abraxas,  each 
nucleus  giving  off  its  two  polar  bodies  and  each  being  independently 
fertilized.  He  suggests  that  gjTiandromorphs  might  arise  from  such 
eggs,  but  did  not  obtain  any  in  the  particular  lines  that  showed  such 
binucleated  eggs.  The  two  gynandromorphs  in  Abraxas  that  Don- 
caster  described  later  (1917),  and  which  are  considered  here  on  page 
85,  he  did  not  attempt  to  explain  by  this  condition. 

The  gynandromorphs  of  Drosophila  have  been  from  the  time  of 
their  first  appearance  in  our  cultures,  about  8  years  ago,  a  subject  of 
general  interest  and  discussion,  especially  by  Muller,  Sturtevant, 
Bridges,  and  Morgan.  Their  relation  to  the  gynandromorphs  in 
bees  and  to  the  theories  of  the  origin  of  the  latter  has  been  constantly 


THE    ORIGIN    OF    GYNANDROMORPHS.  21 

under  discussion.  The  critical  evidence  that  shows  that  they  were 
not  due  to  separation  of  whole  maternal  and  paternal  nuclei  was  first 
obtained  and  published  by  Morgan  (in  1914).  Prior  to  that  time 
Bridges  (1913)  had  published  an  account  of  two  hybrid  gynandro- 
morphs,  and  had  suggested  that  they  were  due  to  somatic  non-dis- 
junction. By  this  term  it  was  meant  at  the  time  that  at  an  early 
embryonic  division  of  a  female  the  two  daughter  halves  of  one  of  the 
X  chromosomes  did  not  disjoin  from  each  other  to  pass,  as  normally, 
into  sister  cells,  but  were  included  in  the  same  cell,  the  other  cell 
not  receiving  its  half.  The  non-disjoining  X  was  assumed  to  divide 
normally  and  the  result  was  an  X  cell  developing  into  male  parts  and 
an  XXX  cell  developing  into  female  parts.  This  hypothesis  served 
to  explain  all  the  facts  known  at  that  time.  Soon,  however,  it  was 
established  (Bridges,  1916)  that  XXX  individuals  are  unable  to  sur- 
vive, and  this  brought  into  question  the  conclusion  that  the  female 
parts  of  gynandromorphs  were  XXX.  This  difficulty  was  later 
avoided  by  the  assumption  of  ''elimination"  (earlier  called  "mitotic 
dislocation,"  Morgan,  1914).  As  already  stated,  this  meant  that  one 
of  the  daughter  X's  was  caught  by  the  mid-plate  and  prevented  from 
taking  its  place  in  either  nucleus. 

There  is  another  class  of  gynandromorphs  (including  here  four  cases) 
in  which  another  procedure  may  account  for  the  results.  Primary 
equational  non-disjunction  occurred,  as  evidenced  by  the  presence 
in  each  of  the  four  gynandromorphs  of  two  X  chromosomes  from  the 
mother,  one  of  these  being  a  non-cross-over  and  the  other  a  cross-over 
X,  as  is  usual  for  XX  eggs  produced  in  this  fashion.  This  XX  egg 
was  then  fertilized  by  an  X  sperm,  giving  an  XXX  individual.  This 
XXX  zygote  is  prevented  from  dying  and  at  the  same  time  converted 
into  a  gynandromorph  by  the  occurrence  of  somatic  reduction  at  the 
first  or  a  very  early  embryonic  division.  In  each  of  the  four  cases 
the  male  parts  of  the  gynandromorph  were  derived  from  one  of  the 
two  maternal  X's,  which  suggests  that  the  essential  feature  of  this 
somatic  reduction  is  the  active  separation  of  the  two  X's  that  came 
from  the  mother  and  the  passive  inclusion  of  the  X  from  the  father 
with  one  or  the  other  of  them.  There  have  been  other  cases  which 
may  support  this  view,  cases  in  which  XX  eggs  equationally  produced 
have  been  fertilized  by  Y  sperm,  and  then  the  two  X's  have  likewise 
reduced,  with  the  result  that  each  cell  gets  one  X,  and  the  entire 
individual  is  converted  into  a  male  which  is  a  mosaic  of  different 
parts  clearly  marked  by  the  character  corresponding  to  the  two  dif- 
ferent X's.  The  difficulty  with  this  view  is  that  it  assumes  that 
reduction  can  take  place  between  two  X's  at  a  cell  division  without 
the  X's  themselves  splitting,  although  all  of  the  other  chromosomes 
do  so  at  this  time — a  situation  for  which  no  support  is  given  by 
cytology.     It  is  to  be  noted  in  this  connection  tliat  all  cases  that  appear 


22  THE   ORIGIN   OF   GYNANDROMORPHS. 

to  belong  to  this  category  are  also  explained  by  the  assumption  that 
the  egg  started  with  two  nuclei,  and  in  the  description  of  cases  both 
of  these  views  are  given  as  alternatives. 

THE  ORIGIN  OF  THE  GERM-CELLS  IN  FLIES. 

In  several  species  of  flies  {Miastor,  Chironomus,  CalUphora)  it  is 
known  that  the  germ-cells  of  the  ovary  or  testis  arise  from  a  single 
cell  at  an  early  stage  in  the  cleavage.  In  Miastor,  for  instance,  when 
the  four  first-formed  nuclei  divide,  one  of  the  eight  daughter  nuclei 
moves  to  one  pole  of  the  egg,  where  it  becomes  surrounded  by  the 
peculiar  protoplasm  of  this  pole  and  subsequently  pinches  off  from  the 
surface  of  the  egg.  From  this  single  cell  by  later  division  arise  all 
of  the  germ-cells.  A  similar  process  has  been  described  for  other 
species  of  flies.  If  this  holds  also  for  Drosophila  it  follows  that  all  of 
the  germ-cells  must  be  either  eggs  or  sperm,  regardless  of  whether 
the  somatic  parts  are  male  or  female.  On  the  other  hand,  if  the  germ- 
cells  in  Drosophila  and  in  the  bee  are  formed  as  in  some  of  the  other 
insects,  i.  e.,  in  the  beetle  Calligrapha  described  by  Hegner,  where  16 
cells  simultaneously  reach  the  polar  field,  it  would  be  possible  for  some 
of  the  cells  to  have  descended  from  one  of  the  first  two  segmentation 
nuclei  and  some  from  the  other.  In  such  a  case,  if  the  first-division 
figure  underwent  elimination,  both  ovaries  and  testes  might  appear 
in  the  same  individual.  In  butterflies  and  moths,  where  many  gynan- 
dromorphs  have  been  dissected,  several  cases  in  which  both  testes  and 
ovaries  occur  are  known.  This  is  also  the  case  in  bees.  A  difference 
in  the  time  of  isolation  of  the  germ-cells  in  these  groups  and  in  Dro- 
sophila may  account  for  the  difference  in  the  results. 

COURTSHIP  OF  GYNANDROMORPHS. 

Sturtevant's  paper  on  sex  recognition  and  sexual  selection  in  Dro- 
sophila gives  a  full  account  of  the  rather  elaborate  courtship  of  this 
fly,  in  which  the  behavior  of  the  two  sexes  is  quite  different.  The  re- 
actions of  an  animal,  male  on  one  side  female  on  the  other,  or  of  one 
that  had  a  female  head  and  a  male  abdomen,  might  be  expected  to 
furnish  interesting  conclusions  as  to  the  relative  importance  of  the 
sense-organs  versus  the  reproductive  organs  in  the  behavior  during 
courtship. 

Sturtevant  tested  6  gynandromorphs.  One  was  male  throughout,  ex- 
cept the  genitalia,  which  were  female.  It  behaved  as  a  male.  Sections 
of  the  abdomen  showed  one  abnormal  egg  present.  Another  had  2  sex- 
combs,  right  and  left,  and  the  right  wing  was  shorter  than  the  left.  The 
abdomen  was  female.  She  produced  at  least  1  egg.  Sections  of  the 
abdomen  showed  2  large  eggs  and  a  degenerate  ovary  present.  She 
courted  and  was  courted,  thus  giving  both  reactions.     A  third  was 


THE   ORIGIN    OF   GYNANDROMORPHS.  23 

male,  except  the  genitalia,  which  were  female.     Sections  showed  an 
abnormal  testis  near  posterior  end.     It  courted  and  was  courted. 

Sturtevant  records  observations  on  three  other  gynandromorphs 
tested  for  sexual  behavior: 

"None  showed  any  certain  indications  of  male  behavior,  but  all  were 
vigorously  courted  by  males.  Of  these  three  gynandromorphs  the  external 
characters  were  as  follows:  (A)  All  female,  except  one  side  of  the  head, 
which  was  male;  (B)  female  on  one  side  of  the  whole  body,  male  on  the 
other  side;  (C)  female,  except  the  genitalia,  which  were  male." 

Duncan  describes  the  behavior  of  a  bilateral  gynandromorph.  Its 
mating  instincts  were  found  to  be  indifferent.  It  was  courted  by 
males  but  would  not  court  females.  The  gonads  were  both  testes 
with  ripe  sperm.  In  a  second  gynandromorph,  the  eyes  were  female, 
but  the  forelegs  had  sex-combs;  one  wing  was  long  (female);  the  ab- 
domen was  male  type,  but  the  genitalia  were  half  male,  half  female. 
Two  ovaries  were  present.  The  fly  was  courted  "assiduously"  by 
males  but  would  not  mate.  A  third  gynandromorph  was  without 
sex-combs  on  the  forelegs,  the  wings  were  the  same  length,  but  the 
abdomen  was  male  on  one  side,  female  on  the  other,  as  were  the 
external  genitalia  also.  Mature  sperm  were  present  in  both  testes. 
This  fly  was  anteriorly  female  and  posteriorly  half  male  and  half 
female.  A  normal  male  courted  this  gynandromorph  when  in  front, 
but  did  not  copulate  wdth  it. 

The  gynandromorph  drawn  in  text-figure  34  was  tested  by  one  of  us 
(Morgan,  T.  H.,  Amer.  Nat.,  1915,  p.  246).  One  side  of  the  head 
and  thorax  is  male,  the  other  side  female.  The  abdomen  is  pig- 
mented above  as  in  a  male  and  there  is  a  penis  below.  When  put 
with  mature  unmated  females  it  did  not  court  them,  although  it  was 
quite  active. 

Attempts  to  breed  from  gynandromorphs  have  been  often  made. 
It  was  not  to  be  expected  that  those  in  which  the  genitalia  were  mixed 
would  successfully  copulate.  Those  with  female  abdomen  have  more 
often  given  offspring.  Since,  as  explained  elsewhere,  the  gynandro- 
morphs with  male  abdomen  would  not  be  expected  to  be  fertile  (be- 
cause the  XO  combination  has  been  shown  to  be  sterile),  the  frequent 
failure  to  obtain  offspring  from  such  males  is  in  accordance  with  ex- 
pectation. On  the  other  hand,  an  occasional  fertile  male  gynandro- 
morph occurs.  In  these  cases  the  combination  was  known  or  suspected 
of  being  XXY,  the  presence  of  the  Y  chromosome  making  the  male 
(XY)  fertile. 

PHOTOTROPISM  IN  MOSAICS  WITH  ONE  WHITE  AND  ONE  RED  EYE. 

On  several  occasions  it  has  been  observed  that  when  a  mosaic  had 
one  red  and  one  white  eye  it  circled  to  the  red  side.  This  beliavior  is 
expected  from  observations  by  McEwen  on  the  light  reaction  of  flies 


24  THE    ORIGIN   OF   GYNANDROMORPHS. 

from  white-eyed  stock.  He  showed  that  these  flies  respond  much  less 
actively  to  hght  than  do  red-eyed  flies.  In  these  red-white  mosaics 
the  red  eye,  giving  a  stronger  positively  phototropic  reaction,  turns 
the  fly  toward  that  side.  Of  course,  if  the  fly  turns  toward  a  single 
source  of  illumination,  such  as  a  window  or  artificial  light,  the  red 
eye  will  soon  pass  into  its  own  shadow  as  the  fly  turns,  and  the  con- 
dition on  the  two  sides  may  become  balanced,  unless  the  general 
illumination  from  the  wall  of  the  room,  for  instance,  is  still  stronger 
than  the  influence  of  the  window's  light  on  the  white  eye.  In  order 
to  avoid  this  complication  the  fly  should  be  kept  on  a  vertical  surface 
held  at  right  angles  to  the  light,  when  its  circus  movements  are  not 
interfered  with  by  the  opacity  of  its  own  body. 

Since  the  male  side  of  the  body,  including  the  legs,  is  generally 
smaller  than  the  female  side,  and  since  the  male  side  is  the  one  that 
has  the  white  eye,  there  is  a  chance  that  the  movements  toward  the 
red  side  are  against  the  stronger  action  of  that  side.  This  complica- 
tion was,  however,  not  realized  in  all  the  cases  in  which  circling  occurred, 
but  since  in  several  of  them  the  legs  on  the  right  and  left  sides  were  the 
same  it  is  practically  certain  that  the  results  are  largely,  if  not  entirely, 
due  to  the  difference  in  stimulus  from  the  two  eyes. 

SEX-LIMITED  MOSAICS. 

By  a  sex-limited  character  (in  contradistinction  to  a  sex-linked) 
we  mean  a  character  that  is  peculiar  to  one  or  the  other  sex,  but  is 
not  necessarily  transmitted  by  means  of  a  gene  in  the  sex  chromosome. 
Such  a  character  is  shown  by  a  stock  called  white  tip,  in  which  the 
pigment  bands  are  absent  from  the  last  segments  of  the  abdomen  in 
the  female  but  not  in  the  male.  In  this  stock  a  gynandromorph 
arose  (text-fig.  6),  male  on  the  left  side  and  female  on  the  right.  On 
the  male  side  the  black  tip  to  the  abdomen  is  present,  although  here, 
as  in  the  stock  itself,  it  is  not  as  black  as  in  the  wild  type.  On  the 
female  side  the  abdomen  has  a  white  end. 

In  this  case  elimination  of  a  sex  chromosome  produced  the  gynan- 
dromorphous  condition,  and  since  in  this  stock  the  female  parts  are 
different  from  the  male,  owing  to  a  factor  presumably  not  in  the  sex 
chromosome,  the  right  side  of  the  gynandromorph  also  shows  this 
peculiarity,  owing  to  its  femaleness. 

A  similar  case  appeared  (No.  2864,  Jan.  1915)  in  a  cross  between  a 
faint-band  female  and  a  star  faint-band  male.  Faint-band  is  a  sex- 
linked  character  which  appears  only  in  the  female.  All  of  the  flies 
of  the  above  cross  were  pure  faint-bands;  but  while  the  females  were 
characterized  by  abdominal  bands  in  which  both  chitinization  and 
pigmentation  were  weak  and  by  short,  slender,  and  irregular  bristles 
throughout,  the  males  could  not  be  distinguished  from  wild  males 
in  appearance.     The  gynandromorph  was  completely  bilateral,  the 


THE   ORIGIN   OF   GYNANDROMORPHS. 


25 


right  side  being  male,  with  sex-comb,  smaller  eye,  wing,  etc.,  and  the 
right  side  of  the  abdomen  with  male  coloration.  The  genitalia  were 
half-and-half  also.  The  interesting  feature  was  that  throughout  the 
female  left  side  the  bristles  were  weak  and  irregular  and  the  bands 
"faint, "  while  the  male  right  side  was  entirely  wild-type  in  appearance. 

Another  striking  case  appeared  (on  March  23,  1916)  among  the 
offspring  of  a  pair,  the  female  of  which  was  heterozygous  for  the  sex- 
limited  character  (" side-abnormal")  and  the  father  was  pure  for  it. 
The  character  "side-abnormal"  is  sex-linked  in  inheritance  and  sex- 
limited  in  appearance,  being  seen  only  in  females.  In  this  mutant 
the  bands  of  the  abdomen  of  the  female  are  "abnormal"  at  the  sides, 
i.  e.,  while  the  mid-dorsal  part  of  the  band  is  normal  the  ends  of  the 
band  where  they  come 
around  the  side  are  cut 
away  irregularly  to 
ragged  points  and  the 
color  is  etched  with 
white  splotches  in  the 
dark.  The  ventral 
plates  are  much 
smaller  and  are  irreg- 
ularly rounded.  In 
the  male  all  parts  are 
as  in  the  wild  flies. 
This  gynandromorph 
(3806)  showed  a  nor- 
mal male  right  half 
of  the  abdomen  and 
a  female  left  half,  with 
all  the  characteristics 
of  the  side-abnormal 
character.  The  ven- 
tral plates  were  full 
and  normal  in  the 
male  parts  and  small 

and  irregular  in  the  female  parts.  Other  evidences  of  maleness  were 
present — a  sex-comb  on  the  right  foreleg  and  a  smaller  right  wing. 

Elsewhere  in  the  text  we  have  described  several  other  cases  involv- 
ing characters  both  sex-linked  and  sex-hmited.  Thus  in  gynandro- 
morph 7530,  page  46,  the  male  eye  on  the  right  showed  marked  devel- 
opment of  the  character  facet,  as  in  the  normal  facet  male,  while  the 
female  left  eye,  also  facet,  could  hardly  be  told  from  wild-type,  as  is 
usual  in  facet  females.  All  gj^nandromorphs  involving  eosin  eye-color 
show  the  Ught  type  of  eosin  in  the  male  eyes  and  the  dark  t>T)e  in  the 
female  eyes. 


Text-figure  6. 


26 


THE   ORIGIN    OF   GYNANDROMORPHS. 


SOMATIC  MOSAICS. 

Somatic  mosaics  can  be  accounted  for  by  autosomal  elimination 
in  the  same  way  that  gynandromorphs  are  accounted  for  by  X-chromo- 
somal  elimination.  Somatic  mosaics  might  also  be  expected  to  arise 
from  binucleated  eggs  and  to  be  as  often  found  as  are  gynandromorphs 
with  the  same  origin.  As  a  matter  of  fact,  we  have  found  only  one 
certain  case,  which  is  less  than  expected  on  the  latter  view.  The  case 
is  as  follows :  -^ 

The  grandmother  was  spineless  (third-chromosome  recessive)  and 
the  grandfather  was  spread  (another  third-chromosome  recessive). 
The  daughters  and  sons  were  wild-type.  A  pair  of  these  gave  a  2 : 1 : 1 : 0 
ratio,  as  expected,  because  of  no  crossing  over  in  the  male. 

One  of  the  granddaughters  (No.  561,  Oct.  3,  1914,  text-fig.  7)  was 
a  mosaic  of  spineless  and  not-spineless.     The  left  side  of  the  thorax 
and  abdomen  and  the  left  wing  and  the  middle 
and  last  left  leg  were  spineless.     The  rest  of  the 
female  (including  all  of  the  head  and  left  foreleg) 
had  long  bristles  and  hairs  of  the  wild  type. 

Simple  eUmination  of  the  third  chromosome  from 
the  spread  parent  would  explain  this  case  were  it 
not  that  the  existence  of  an  individual  lacking  an 
autosome  is  doubtful,  because  none  have  as  yet 
appeared  through  autosomal  non-disjunction.  On 
the  alternative  view  of  a  binucleated  egg,  one 
nucleus  contained  the  spineless  third  chromosome, 
the  other  a  spread-bearing  chromosome ;  both  nuclei 
were  fertilized  by  X  sperm  bearing  the  spineless 
X  chromosome,  and  gave  the  female  spineless  on  the 
left  side  and  wild-type  on  the  right  side. 

The  fact  that  the  overwhelming  number  of  hy- 
brid mosaics  are  gynandromorphs,  involving  there- 
fore the  sex  chromosome,  can  not  be  explained  as  due  to  failure  to 
discover  autosomal  mosaics  if  they  occurred.  In  most  of  our  cases 
these  would  be  just  as  striking  as  in  the  cases  where  the  sex  chromo- 
somes are  involved.  Evidently  some  peculiarity  in  the  separation  of 
the  halves  of  the  sex  chromosomes  makes  the  elimination  of  one  of 
the  daughter  halves  more  probable  than  in  the  case  of  other  chro- 
mosomes. Such  a  supposition  is,  of  course,  in  harmony  with  the  pecu- 
liar behavior  of  the  sex  chromosome  at  the  reduction  division  of  the 
male,  at  least  when  it  lags  on  the  spindle.  On  the  other  hand,  when 
it  does  divide,  as  in  the  female,  no  such  peculiarity  is  recorded,  and 
it  is  this  reduction,  rather  than  the  former  one,  that  we  need  for  com- . 
parison. 


Text-figure  7. 


THE    ORIGIN   OF   GYNANDROMORPHS.  27 

SOMATIC  MUTATION. 

That  mutation  may  take  place  in  somatic  cells  comparable  to  the 
mutation  process  in  the  germ- tract  can  not  be  doubted.  The  bud- 
sports  long  familiar  to  botanists  probably  furnish  in  some  instances 
examples  of  this  sort;  but  the  best  authenticated  cases  are  the  modern 
ones  that  have  been  analyzed  by  recognized  genetic  methods,  P'ew 
examples  are  known  to  zoologists;  the  monsters,  freaks,  and  duplica- 
tions that  are  frequently  found  are  generally  due  to  environmental 
effects  on  the  embryo. 

If  somatic  mutation  occurs  in  only  one  chromosome  of  a  pair,  as 
seems  to  be  the  case  with  germinal  mutations,  the  immediate  result 
will  not  be  seen  except  when  the  mutation  is  dominant.  In  the  case 
of  mutation  in  the  germ-tract,  a  recessive  gene  in  one  chromosome 
of  a  pair  may  Hkewise  not  have  opportunity  at  first  to  express  itself, 
but  if  it  is  carried  to  one  of  the  offspring  it  will  there  become  multiplied 
and  get  into  daughters  and  sons  (or  in  hermaphroditic  species  into 
pollen  and  ovules).  Chance  union  of  the  gametes  that  contain  the 
mutated  chromosomes  will  later  bring  even  the  recessive  genes  to 
expression.  It  is  more  probable,  therefore,  that  recessive  mutations 
will  appear  in  the  sexually  reproducing  species  more  readily  than 
in  those  with  vegetative  reproduction,  except  where  the  latter  are 
already  heterozygous.  The  same  comparison  may  be  made  between 
parthenogenetic  species  and  sexual  ones.  In  the  former,  a  recessive 
mutation  appearing  in  one  chromosome  of  a  pair  will  have  no  oppor- 
tunity to  show  effects,  and  the  line  may  be  lost  by  chance  alone. 
Preservation  will  be  favored  only  if  the  heterozygous  state  has  an  ad- 
vantage over  the  original  form.  Sexual  reproduction,  therefore,  has 
the  advantage  that  every  recessive  mutation  will  have  a  far  better 
chance  of  showing  itself  as  a  character  modification  and,  if  beneficial, 
of  being  preserved  by  natural  selection.  In  fact,  if  it  could  be  shown 
that  a  preponderant  number  of  recessive  mutations  have  furnished 
the  material  for  evolution,  it  might  possibly  appear  that  we  had  some 
hint  as  to  how  the  process  has  come  to  be  such  an  almost  universal 
method  of  propagation.  On  the  other  hand,  dominant  mutations 
might  flourish,  as  well  by  the  one  as  by  the  other  method. 

The  best  authenticated  case  of  somatic  mutation  in  plants  is  that 
described  by  Emerson,  who  has  brought  forward  convincing  evidence 
that  in  corn  a  gene  for  certain  types  of  variegation  (striped  seeds) 
mutates  not  infrequently  to  a  gene  for  uniform-colored  grain.  The 
gene  for  medium  variegated  "mutates  much  more  frequently  than 
that  for  very  light  variegation. "  By  crossing  pLants  from  the  nuitated 
grains  to  pure  recessive  types  Emerson  has  shown  tliat  when  the 
mutation  occurs  it  involves  only  one  member  (at  a  time)  of  the  pair 
of  allelomorphs  in  question.  In  these  cases  the  mutation  takes  place 
in  cell  lines  (subepidermis)  that  may  ultimately  contribute  both  to 


28  THE   ORIGIN   OF   GYNANDROMORPHS. 

the  germ-tract  and  to  the  soma.  Through  the  former,  inheritance 
becomes  possible,  through  the  latter  the  effects  of  the  mutation  be- 
come visible  only  on  the  plant  in  which  the  mutation  took  place. 
There  are  other  mutative  changes  in  corn  that  Emerson  describes  in 
which  the  effect  is  only  in  the  epidermal  cells;  hence,  while  it  becomes 
visible  in  the  plant  in  which  it  has  taken  place,  it  is  not  inherited,  since 
the  germ-tract  does  not  come  from  this  part  of  the  plant. 

In  the  course  of  our  work  on  Drosophila  a  few  flies  have  appeared 
with  characters  which  seem  to  have  arisen  by  somatic  mutation.  If, 
as  there  is  reason  to  suppose,  the  mutation  changes  that  gave  rise  to 
them  appeared  in  only  one  chromosome,  the  change  must  either  have 
been  dominant  or,  if  recessive,  in  the  single  X  chromosome  of  the 
male.  Since  visible  mutations  in  the  sex  chromosome  have  been 
shown  to  be  at  least  four  times  as  frequent  as  dominants  in  all  of  the 
chromosomes  together,  the  chance  that  these  sporting  characters  are 
dominants  is  smaller  than  that  they  are  recessive  and  in  the  sex 
chromosome.  In  support  of  the  latter  is  the  fact  that  nine  out  of  ten 
of  the  sporting  characters  look  like  known  sex-linked  genetic  char- 
acters, and  more  important  still  is  the  fact  that  all  the  cases  so  far 
found  are  males. 

(1)  One  of  these  somatic  sports  is  shown  in  plate  1,  figure  4.  The 
right  side  of  the  body  is  pale,  almost  white.  The  history  of  this  fly 
is  as  follows '} 

One  of  the  X  chromosomes  of  the  mother  contained  the  genes  for  lethal  7 
and  for  forked,  the  other  X  the  genes  for  yellow  and  for  white.  The  X 
chromosome  of  the  father  carried  the  genes  for  yellow  and  for  white.  The 
fly  was  a  yellow  white  forked  male  throughout,  but  the  right  side  of  the 
thorax,  the  right  wing,  and  the  right  side  of  abdomen  were  pale,  almost  white, 
as  shown  in  the  drawing.  Testes  were  present,  with  sperm.  The  pale  light 
side  is  clearly  due  to  somatic  mutation,  since  no  such  pale  body-color  was 
present  in  the  cross  or  was  known  elsewhere.  Whether  the  mutation  oc- 
curred in  the  X  (if  recessive)  or  in  an  autosome  (if  dominant)  is  undeter- 
minable, since  the  fly  was  not  bred. 

(2)  In  another  case  (II 108,  Oct.  21,  1913),  the  left  side  of  the  body, 
at  least  for  a  middle  section,  is  brown  in  color,  looking  like  the  double 
recessive  yellow  black  (text-fig.  8).     The  fly  had  the  following  history: 

Some  F2  blacks  from  the  cross  of  black  by  jaunty  (both  second-chromo- 
some) were  inbred  in  an  attempt  to  secure  the  double  recessive  black  jaunty. 
One  of  the  F3  black  males  had  the  left  side  of  its  thorax  and  abdomen,  left  wing, 
and  left  legs  colored  like  the  double  recessive  yellow  black.  It  was  at  once 
assumed  that  mutation  to  yellow  had  occurred  in  the  early  embryo  in  the 
cells  which  gave  rise  to  the  left  side.  A  test  was  made  to  see  whether  the 
germ-cells  carried  the  mutant  gene.  The  mosaic  male  was  outcrossed  to 
a  black  female  and  gave  only  black  offspring  (M69,  black  9  27,  black  cf  23). 
Three  pairs  and  a  mass-culture  of  these  Fi  flies  were  inbred  and  gave  a  total 

^No.  2493;  November  20,  1915. 


THE   ORIGIN   OF   GYNANDROMORPHS. 


29 


of  152  black  9  and  147  black  cT,  with  no  yellow-black  offspring.  Evidently, 
then,  the  testes  came  from  a  cell  which  had  not  mutated.  While  the 
"brown"  color  of  the  mosaic  was  like  that  produced  by  yellow  acting  with 
black,  it  is  possible  that  the  mutant  gene  was  not  the  yellow  already  known, 
but  a  new  yellow. 

(3)  Among  the  grandchildren  of  the  kst  somatic  sport  a  fly  was 
found  with  a  wing  of  an  unusual  type  (text-fig.  9).     This  wing  was 
about  half  the  usual  length  and  had  almost  exactly  the  form  of  min- 
iature, but  there  was  none  of  the  dark  color  normally  present  in 
miniature  wings.     This  wing  seems  to  have  been  a  new  mutant  type, 
the  mutation  having  occurred  in  the  early  embryonic  cells  of  the  fly. 
There  have  been 
quite  a  number  of 
such  occurrences, 
some,    as   in  the 
present  case,  giv- 
ing striking  differ- 
ences. 

(4)  A  fly  ap- 
peared in  vestigial 
stock  (August  13, 
1912)  with  one 
normal  wing  (text- 
fig.  10).  It  was 
described  as  a  case 
of  somatic  atav- 
ism. An  alterna- 
tive view  is  also 
possible,  viz,  that 
a  somatic  muta- 
tion occurred  else- 
where, i.  e.,  in  an- 
other chromosome  or  in  another  region  of  the  second  chromosome, 
of  such  a  sort  that  it  neutralized  the  effect  of  both  genes  for  vestigial. 
In  the  cells  containing  this  mutant  gene  the  conditions  for  normal 
wings  are  again  restored. 

(5)  a  nd  (6)  Two  further  cases  of  mutation  in  the  male  were  found 
by  Sturtevant  (not  published);  both  were  males  throughout;  one  had 
forked  bristles  on  one  side  of  the  body,  although  there  were  no  forked 
flies  in  the  immediate  ancestry.  The  other  had  a  dark  body-color 
on  part  of  the  thorax,  there  being  no  sex-hnked  dark  body-color  in 
the  ped  igree.     Neither  fly  was  tested. 

(7)  I  n  a  stock  pure  for  red  eyes,  miniature  wings,  and  j^ellow  body- 
color  a  fly  appeared  with  all  the  characters  of  its  race  except  that  one 
eye  w  as  white  with  a  fleck  of  red  at  its  posterior  edge  (text-fig.  11). 


Text-figure  8. 


TEXT-nOCRE  9. 


30  THE    ORIGIN   OF   GYNANDROMORPHS. 

Since  there  was  no  white  in  the  stock,  the  white  eye  must  have  come  by 
mutation  and  possibly  by  mutation  to  a  sex-Hnked  white-eyed  gene. 

(8)  In  a  mating  in  which  both  parents  were  pure  bar-eyed  flies  a 
male  appeared  (1917)  (text-fig.  12)  in  which  both  eyes  were  round 
and  in  addition  one  eye  was  three-quarters  white,  and  the  other  had 
a  fleck  of  white  in  it.  A  germinal  mutation  in  the  mother  of  bar  to 
round  eye  must  have  taken  place,  as  shown  by  the  fact  that  when  the 
fly  was  bred  it  produced  only  normal-eyed  offspring.  Since  this 
male  was  normal,  it  must  have  come  from  the  union  of  a  Y-bearing 
sperm  and  an  X  egg.  Since  the  bar  gene  is  carried  by  the  X  chromo- 
some, it  follows  here  that  mutation  must  have  occurred  in  one  sex 
chromosome  of  the  mother.  It  is  significant  in  this  connection  to  call 
attention  to  the  fact  that  bar-eye  not  infrequently  mutates  (reverts)  to 
normal,  as  May  has  clearly  proven. 

The  other  change  to  white  was  due 
to  a  somatic  mutation. 

(9)  In  stock  pure  for  black  and 
for  miniature  and  impure  for  white 
and  for  red  eyes  a  male  appeared 
that  had  one  white  eye  (text-fig.  13). 
It  might  appear  here  that  simple 
elimination  in  a  heterozygous  female 
would  account  for  the  white  eye,  but 
if  the  fly  arose  in  this  way  the  rest 
of  it  should  be  female.  Double  elim- 
ination will,  however,  give  a  result 
of  this  kind,  i.  e.,  a  red  X  is  lost 
from  one  half  and  a  white  X  from  Text-figure  lo. 
the  other  side,  leaving  both  parts 

male,  one  red,  the  other  white.  If,  on  the  other  hand,  the  fly  started 
as  a  red-eyed  male  and  dislocation  occurred,  so  that  most  of  the  fly 
had  an  X,  the  other  part  a  Y  chromosome,  the  expectation,  based  on 
the  evidence  from  nondisjunction,  would  be  that  the  male  part  would 
die.  However,  it  might  be  claimed  that  the  evidence  appHes  to  the 
fly  as  a  whole  and  not  to  the  survival  of  a  small  part  of  the  body, 
which  might  very  well  be  capable  of  living.  But  we  should  expect  the 
absence  of  X  to  carry  other  consequences  in  its  train  besides  loss  of 
eye-color,  so  that  this  explanation  seems  improbable.  A  third  explan- 
ation is  that  of  somatic  mutation.  It  is  not  possible  to  decide  between 
the  assumption  of  double  elimination  and  that  of  somatic  mutation. 

(10)  A  somewhat  similar  case  is  shown  in  the  male  figured  in  plate  1, 
figure  5.  Its  ancestry  is  not  now  a  matter  of  record,  but  probably 
it  arose  in  red-eyed  bifid  stock  that  we  had  at  the  time.  If  so,  double 
elimination  is  excluded  and  the  fly  must  have  arisen  by  mutation  in 
the  sex  chromosome. 


THE   ORIGIN    OF   GYNANDROMORPHS. 


31 


It  is  a  matter  of  great  interest  to  find  tliat  all  the  ten  cases  of  somatic 
mutation  that  we  have  recorded  in  Drosophila  have  been  males.  The 
significance  of  this  was  not  appreciated  until  the  material  had  been 
sorted  out  for  other  purposes.  It  probably  means  that  a  recessive 
somatic  mutation  takes  place  in  the  sex  chromosome  and  shows  at 
once  in  a  male  in  those  parts  of  the  body  whose  cells  contain  the  mutant 
gene  because  the  male  has  only  one  sex  chromosome.  Should  a  reces- 
sive mutation  occur  in  the  X  chromosome  of  a  female  its  effect  would 
not  appear  in  the  soma  because  the  normal  allelomorph  would  conceal  it. 
It  is  interesting  to  apply  this  point  of  view  to  certain  results  in  Lepi- 
doptera  in  which  mosaics  or  gynandromorphs  have  been  recorded  that 
carry  in  parts  of  the  body  characteristics  that  are  known  to  occur, 
although  rarely,  in  varieties  of  sports  of  the  species. 


Text-figuke  11. 


Text-figure  12. 


Text-figure  13. 


Among  these  a  number  have  been  described  with  one  half  of  the 
body  of  one  species  and  the  other  half  of  a  varietal  type  of  the  same 
species.  In  some  cases  the  variety  is  so  rare  that  there  might  seem 
to  be  no  question  of  a  hybrid  cross  involved,  since  this  in  itself  would 
be  rare,  and  that  both  this  and  a  later  mosaic  condition  result  is  beyond 
reasonable  probability.  An  alternative  view  would  be  that  of  somatic 
mutation.  If  such  were  the  explanation  we  should  expect  the  indi- 
vidual to  be  female  and  the  mutation  to  have  occurred  in  the  single 
Z  chromosome. 

In  the  cases  brought  together  by  Cockayne,  in  which  the  same 
individual  is  partly  one  species,  partly  a  variety  (1915,  pp.  87-90), 
there  are  about  10  such  cases  recorded  as  females,  2  as  males;  in  12 
cases  no  sex  is  stated  by  Cockayne.  If  further  examination  of  the 
original  sources  shows  as  high  a  percentage  of  females  as  in  the  recorded 
cases,  the  evidence  is  in  favor  of  the  interpretation  suggested  above. 
The  males  call  for  another  interpretation,  and  each  such  case  will 
need  special  examination. 


32  THE   ORIGIN   OF   GYNANDROMORPHS. 

These  cases  are  not  to  be  confused  with  mutation  in  the  germ- 
tract,  where,  in  a  sense,  the  reverse  situation  is  realized,  for  while  in 
Drosophila  the  mutation  of  a  sex-linked  character  in  one  female  chromo- 
some appears  immediately  in  one  (or  more)  of  her  sons,  the  mutation 
itself  occurred  first  in  the  female.  Conversely,  in  moths,  if  a  germ- 
tract  mutation  took  place  in  the  male  it  would  show  immediately  in 
one  or  more  daughters.  The  well-known  case  of  Abraxas  grossulariata 
may  be  taken  to  show  why  mutation  taking  place  in  a  male  is  expected 
to  show  first  in  the  female  and  not  in  the  male  offspring.  The  genetic 
evidence  for  Abraxas  indicates  that  the  female  has  one  sex  chromo- 
some, the  male  two.  The  aberrant  form  lacticolor  is  found  occasion- 
ally in  nature  and  is  always  female.  A  mutation  to  lacticolor  in  a 
Z  chromosome  of  the  male  would  give  rise  to  a  daughter  if  this  sperm 
fertilized  a  not-Z  egg  that  would  at  once  show  the  sex-linked  character 
lacticolor. 

MOSAICS  IN  PLANTS. 

The  cause  of  variegation  in  plants  is  too  involved  and  obscure^ 
to  attempt  to  discuss  in  this  connection.  On  the  other  hand,  the 
occurrence  of  bud-sports  is  generally  recognized  as  due  to  somatic 
mutation  which  may  include  the  germ-tract  also.  The  frequent  occur- 
rence of  bud  variation  in  the  cultivated  forms  of  the  foliage  plant 
Coleus  has  recently  been  studied  by  Stout,  who  has  obtained  from  a 
single  plant  (and  its  clones)  a  number  of  types  differing  both  in  color 
and  form  of  the  leaves.  The  cultivated  varieties  have  arisen  through 
hybridization.  Three  interpretations  suggest  themselves  as  possible. 
Elimination  of  the  chromosomes  of  the  hybrid  might  account  for  the 
results,  but  no  information  as  to  the  chromosomes  in  the  different 
types  is  available.  If  any  of  the  colors  are  due  to  cytoplasmic  plastids, 
their  irregular  distribution  might  also  be  responsible  for  the  result. 
Thirdly,  the  change  might  be  due  to  a,  mutation.  If  the  types  studied 
are  complex  hybrids  with  one  or  more  heterogeneous  pairs  of  chromo- 
somes, a  change  in  one  gene  of  one  chromosome  might  bring  about 
directly  a  \'isible  change  in  the  color.  Until  more  critical  Mendelian 
work  is  done  it  is  not  possible  to  reach  any  plausible  or  even  probable 
conclusion.  It  might  be  possible  to  analyze  the  results  more  closely 
if  we  knew  what  kinds  of  offspring  arise  from  the  original  plant  and 
its  varieties.  Owing  to  the  complex  nature  of  the  plants  this  pro- 
cedure offers  difficulties.  A  few  facts  are  given  by  Stout.  He  states 
that  "plants  grown  from  seed  give  wide  variations  ....  Many 
of  the  types  that  had  appeared  as  bud  variations  appeared  also  in  the 
seed  progenies." 

Winkler  produced  mosaics  by  grafting  tomato  and  nightshade,  which 
are  now  supposed  to  be  due  to  a  combination  of  the  tissues  of  the 

'  Except  in  the  case  of  Pelargonium  and  of  Mirahilis,  where  Baur  and  Correns  have  shown 
that  the  mosaics  are  caused,  in  some  instances  at  least,  by  plastid  assortments. 


THE    ORIGIN   OF   GYNANDROMORPHS.  33 

two  plants — the  epidermis  of  one  species  and  a  core  of  the  other  s{x?cie8. 
The  mosaic  shown  in  Cytisus  adami,  a  hybrid  resulting  from  fi;raftinK 
Cytisus  purpureus  and  Laburnum  vulgare,  seems  also  to  be  due  to  a 
similar  sort  of  combination.  In  animals  mosaics  have  been  produced 
in  hydra  by  King  by  grafting  pieces  of  a  deep-green  race  on  a  light 
one,  and  by  Whitney  by  destroying  the  green  pigment  of  one  indi- 
vidual and  grafting  pieces  of  it  onto  a  normal  green  hydra.  In  tad- 
poles combinations  of  different  species  caused  by  grafting  have  been 
made  by  Born,  Harrison,  Morgan,  and  others.  A  result  strictly 
comparable  to  the  periclinal  chimaeras  of  plants  has  been  reached  by 
grafting  a  piece  of  the  tail  of  one  species  on  to  the  amputated  stump 
of  another  species.  As  the  new  tail  grows  the  skin  of  the  stock  is 
carried  out  over  the  core  derived  from  the  graft,  and  as  a  result  an  organ 
is  formed  with  an  outer  layer  of  one  and  a  core  of  another  species. 

The  mosaic  seeds  of  corn  that  are  striped  with  red  and  white  have 
been  shown  by  Emerson  to  arise  through  a  mutation  in  the  gene  for 
striping.  The  ''half-and-half"  mosaic  grains  that  have  been  recorded 
by  Correns  (1899),  Weber  (1900),  East  and  Hayes  (1911),  Emerson 
(1915),  and  Collins  (1919)  have  been  variously  accounted  for — re- 
calling the  different  interpretations  that  have  been  advocated  for 
gynandromorphs  in  animals.  Emerson  (1915)  reviews  these  theories 
and  advances  the  explanation  of  somatic  mutation.  It  seems  not 
improbable  that  elimination  will  account  for  those  mosaics  in  which 
the  triploid  endosperm  nucleus  is  involved. 

CLASSIFICATION  AND  DESCRIPTION  OF  GYNANDROMORPHS 

OF  DROSOPHILA. 

The  main  group  includes  the  gynandromorphs  that  are  adequately 
explained  by  chromosomal  elimination.  It  is  subdivided  according  to 
the  type  of  gynandromorph  into :  (1)  those  approximately  bihiteral,  (2) 
those  mainly  female,  (3)  those  mainly  male,  (4)  those  in  which  the 
type  is  largely  "fore  and  aft,"  and  (5)  those  in  which  the  mother  was 
known  to  have  been  an  XXYfemale,  but  in  which  simple  elimination 
is  sufficient  to  account  for  the  results.  Another  group  (6)  includes 
those  in  which  the  distribution  of  parts  is  irregular.  These  types  are 
only  approximations  and  by  no  means  mutually  exclusive;  it  is  often 
somewhat  difficult  to  decide  to  which  type  a  specimen  belongs. 

The  highly  interesting  group  of  special  cases  (7)  is  undi\ided, 
though  it  calls  for  three  or  four  different  genetic  explanations,  based, 
however,  on  special  modes  of  distribution  of  the  sex  chromosomes. 
In  the  Appendix  are  included  those  cases  in  which  our  records  are 
incomplete  as  to  parentage  or  in  which  the  specimen  has  been  lost, 
so  that  the  description  is  sketchy.  This  grou])  contains  many  of  the 
very  early  gynandromorphs.  To  this  subdivision  is  added  a  brief 
review  of  previously  pubhshed  gynandromorphs  in  Drosophila. 


34 


THE    ORIGIN   OF   GYNANDROMORPHS. 


Within  each  subdivision  the  arrangement  of  the  cases  is  according 
to  the  order  of  discovery,  that  is,  by  date,  except  that  the  colored 
figures  are  taken  out  of  order  and  described  first  in  each  group. 

Each  case  is  known  by  a  number,  which  is  usually  that  of  the  culture 
bottle  in  which  the  gynandromorph  was  found,  but  in  some  cases 
letters  or  small  numbers  are  used,  which,  however,  correspond  to  the 
bottle  in  which  the  specimen  is  preserved  or  the  order  in  which  the 
descriptions  were  first  arranged.  The  date,  the  finder,  and  the  type 
of  illustrations  are  also  indicated  on  the  number  line. 

The  information  on  each  case  is  then  given  in  the  order.  Parentage, 
Description,  and  Explanation.  In  many  of  the  cases  the  explanation 
is  followed  by  a  diagram  showing  at  the  left  the  two  X  chromosomes  of 
the  zygote,  which  at  the  same  time  represent  the  female  parts  of  the 
gynandromorph,  and  at  the  right  the  single  X  that  is  left  after  elimina- 
tion, which  gives  the  constitution  of  the  male  parts.  In  case  somatic 
reduction  was  involved  the  leftmost  set  of  chromosomes  represents 
the  initial  condition  of  the  zygote,  and  the  other  two  sets  to  the  right 
the  resulting  two  conditions,  whether  male  or  female. 

A  knowledge  of  the  order  and  the  relative  spacing  of  the  genes  along 
the  chromosome  is  indispensable,  and  we  have  therefore  made  a  list 
of  the  sex-linked  mutants  mentioned,  with  their  symbols  and  the 
approximate  locus  of  each : 


Mutant. 

Symbol. 

Locus. 

Mutant. 

Symbol. 

Locus. 

Sable  duplication .  .  . 
Lethal  6 

S 

le 

y 

h 

w 

w« 

w* 

N 
fa 
b« 

h 

0.0 

-0.004 

0.0 

0.3 

\      1-1 

1       2.6 
6.3 

/       7.0 

12.5 

Club 

Cut 

c« 
t 

V 

m 
h 

a 
g 

u 

r 

f 

B 
f« 

16.7 
20.0 
27.5 
33.0 
36.1 
38.0 
43.0 
44.4 
45  ± 
49.0 
55.1 
56.5 
57.0 
59.5 
65=fc 

Yellow 

Tan 

Lethal  7 

Vermilion 

White 

Miniature 

Eosin 

Lethal  9 

Blood 

Sable 

Cherry 

Garnet 

Notch 

Rugose 

Facet 

Lethal  4 

Bifid 

Rudimentary 

Forked 

Bar 

Ruby 

Claret 

Crimson 

Lethal  2 

Fused 

Cleft 

The  figures  in  the  plates  are  camera-lucida  drawings  of  etherized 
living  flies,  but  in  the  following  descriptions  of  the  gynandromorphs 
diagrams  only  are  given  (except  in  rare  instances).  These  diagrams 
were  made  from  the  flies  themselves,  which  are  preserved  in  alcohol. 
All  drawings  and  diagrams  were  made  by  Miss  Edith  M.  Wallace, 
to  whose  skill  and  accuracy  they  bear  witness. 


PLATE  2 


\ 


TtHwC  J 


\ 


■    4;i 


X!# 


^-  s 


\y<- 


v..  \1.  w 


M.I.ACK    I'mx 


GYNANDROMORPHS   OF    DROSOPHILA 


THE    ORIGIN   OF   GYNANDROMORPHS.  35 

Approximately  Bilateral  Gynandromorphs. 
No.  Giad2.     Feb,  1914.     E.  M.  Wallace.     Plate  2,  Figure  1  (colored  drawing). 

Parentage. — The  mother  wavS  a  white-eosin  compound  female  from  the  cross 
of  a  yellow  white  female  to  an  eosin  male.     The  father  was  a  yellow  white  male. 

Description. — The  entire  head,  the  right  half  of  the  thorax  and  of  the  ab- 
domen, the  right  wing,  and  all  of  the  right  legs  were  gray  and  female.  Both 
eyes  were  white-eosin  compound  and  therefore  female,  which  was  in  agree- 
ment with  the  gray  color  and  black  bristles  of  the  whole  head.  The  genitalia 
were  apparently  entirely  female.  The  left  side  of  the  thorax  and  of  the 
abdomen,  the  left  wing,  and  all  of  the  left  legs  were  yellow  in  body-color, 
smaller,  and  male.  There  was  a  sex-comb  on  the  left  side  only.  The  gynan- 
dromorph  failed  to  produce  offspring  when  tested. 

Explanation. — An  egg  with  the  eosin-bearing  X  was  fertilized  by  the  X 
sperm  bearing  the  genes  for  yellow  and  white.  The  zygote  was  therefore 
female,  and  the  female  parts  of  the  gynandromorph  have  this  constitution. 
At  the  first  segmentation,  division  elimination  of  a  maternally-derived  eosin- 
bearing  X  occurred,  giving  rise  to  a  cell  with  only  a  yellow  white  X.  The 
parts  descended  from  this  cell  were  male  and  showed  the  yellow  body-color 
corresponding  to  the  yellow  white  chromosome.  Since  neither  of  the  eyes 
was  male,  the  white  eye-color  had  no  chance  to  show  on  the  left  side. 

w 
I 


y  w  y  w 

No.  GaCisa.     Feb.  1914.     E.M.Wallace.     Plate  2,  Figure  2  (colored  drawing). 

Parentage. — A  mass  culture  of  the  white-eosin  compound  females  (eosin  in 
one  X  and  yellow  white  in  the  other,  from  gynandromorph  G2C19  above)  out- 
crossed  to  yellow  white  males  produced  a  further  gynandromorph  (G2C190). 

Description. — The  gynandromorph,  while  yellow  and  white  throughout,  was 
a  strict  bilateral  gynandromorph,  including  genitalia  and  antennae.  The  right 
side  was  male  throughout,  as  evidenced  by  sex-comb,  smaller  size  of  bristles 
and  of  all  parts  such  as  eye,  thorax,  wing,  legs,  and  abdomen,  and  by  the  male 
coloration  of  right  side  of  the  abdomen.  The  gynandromorph  was  tested  but 
gave  no  offspring.     Sections  showed  slightly  developed  ovaries  on  both  sides. 

Explanation. — An  egg  containing  the  X  with  the  genes  for  yellow  and  white 
was  fertilized  by  an  X  sperm  likewise  carrying  the  genes  for  yellow  and  white. 
Elimination  at  the  first  segmentation  division  of  a  maternal  or  of  a  paternal 
X,  gave  a  cell  with  a  single  X,  from  which  is  descended  the  male  right  side. 

y  w  yw 


yw 

No.  77.     March  10,  1914.     C.  B.  Bridges.     Text-figure  14  (diagram). 

Parentage. — The  mother  was  homozygous  for  eosin  and  heterozj'gous  for  a 
non-sex-linked  gene  "cream,"  which  is  a  specific  dilutor  for  eosin  (Bridges, 
1916).     The  father  had  the  same  constitution. 

Description. — The  gynandromorph  was  completely  bilateral  "from  head 
to  tail."  The  right  side  was  male  with  a  sex-comb  and  smaller  jKirts.  The 
abdomen  had  the  female  coloration  above,  but  below  was  divided  iialf  and 
half,  as  were  the  genitalia.     The  eyes  were  both  "cream,"  that  is,  of  diluted 


36 


THE    ORIGIN   OF   GYNANDROMORPHS. 


eosin  color.     The  right  male  eye  was  much  lighter  than  the  female  left  eye, 
as  is  the  rule  with  eosin  even  when  diluted. 

Explanation. — Both  egg  and  sperm  carried  the  genes  for  eosin  and  cream. 
Elimination  of  the  paternal  or  of  the  maternal  X  occurred.  Presumably  the 
autosome  carrying  the  cream  gene  behaved  normally  as  in  all  known  cases, 
but  this  case  is  not  diagnostic,  since  the  fly  was  homozygous  for  cream. 


w^ 


w^ 


w^ 


Text-figure  14. 


Text-figure  15. 


Text-figure  16. 


No.  1-5.     A.M.Brown.     April  9,  1914.     Plate  2, Figure 4  (colored  drawing) . 

Parentage. — The  grandmother  was  homozygous  for  vermilion  and  hetero- 
zygous for  a  lethal.  The  grandfather  was  eosin-miniature.  A  gynandro- 
morph  was  produced  by  one  of  their  wild-type  daughters  which  had  been 
out-crossed  to  an  eosin-miniature  male. 

Description. — The  right  side  was  male  throughout  with  an  eosin  (male 
color)  eye  and  miniatm-e  wing.  A  sex-comb  was  present  on  the  right  foreleg. 
The  left  side  was  entirely  female,  with  red  eyes  and  a  long  wing. 

Explanation. — A  non-cross-over  egg  containing  the  wild-type  X  was  fertil- 
ized by  an  X  sperm  with  genes  for  eosin  and  for  miniature.,  Ehmination  of 
one  of  the  maternal  X's  left  the  male  parts  eosin-miniature. 


w 


m 


w^ 


m 


No.  195.     April  27,  1914.     C.  B.  Bridges.     Text-figm-e  15  (drawing). 

Parentage. — One  X  chromosome  of  the  mother  carried  the  gene  for  white 
eye-color  and  the  other  X  the  genes  for  eosin  and  for  lethal  4.     The  X 
chromosome  of  the  father  carried  the  gene  for  sable. 


THE   ORIGIN   OF   GYNANDROMORPHS.  37 

Description. — The  right  side  of  the  gynandromorph  was  male,  with  a 
white  eye  (with  a  fleck  of  red  in  it)  and  a  sex-comb.  The  right  wing  was 
smaller.     The  genitalia  were  mainly  male,  but  also  with  some  female  parts. 

Testes  were  found  in  sections  of  the  abdomen,  with  plenty  of  sperm. 

Explanation. — An  egg  containing  the  white  X  wa-s  fertilized  by  a  sable- 
bearing  X  sperm.  A  paternal  sperm  suffered  elimination,  leaving  the  white- 
bearing  X  to  produce  the  male  side.  The  female  side  is  wild-type,  since  one 
X  has  the  normal  allelomorph  for  white  (viz,  red  eye),  and  the  other  X  the 
normal  allelomorph  for  sable  (viz,  wild-type  body-color) . 

w  w 


No.  1373.     February  22, 1915.     C.  B.  Bridges.     Text-figure  16  (diagram). 

Parentage. — One  of  the  X  chromosomes  of  the  mother  carried  the  genes 
for  eosin  and  for  vermilion,  and  the  other  X  the  genes  for  sable  body-color 
and  forked  bristle.  The  X  chromosome  of  the  father  carried  the  dominant 
gene  for  bar. 

Description. — The  left  side  of  the  gynandromorph  was  male  throughout, 
being  of  smaller  size  in  head,  thorax,  abdomen,  wing,  bristles,  and  legs,  and 
having  a  sex-comb.  The  right  eye  was  e  'sin-vermilion  in  color  and  not- 
bar.  The  coloration  of  the  abdomen  was  male  on  the  left  side  at  the  tip, 
and  the  genitalia  were  very  largely  male.  The  right  side  was  female,  with 
a  red-bar  eye.  The  abdomen  was  sectioned  and  found  to  contain  a  pair  of 
poorly  developed  ovaries. 

Explanation. — An  egg  containing  the  X  chromosome  with  genes  for  eosin 
and  for  vermilion  was  fertilized  by  the  bar-bearing  X  sperm.  Elimination  of 
a  paternal  X  chromosome  left  the  eosin-vermilion-bearing  X  to  produce  the 
male  side,  while  the  female  side  contained  the  dominant  allelomorphs  for  these 
two  genes,  as  well  as  the  dominant  gene  for  bar  eye  in  the  female  XX  complex. 


B 

No.  D.     From  Lethal  2  Stock.     May  1,  1915.     E.  M.  Wallace. 

Text-figure  17  (diagram). 

Parentage. — The  wild-type  mother  carried  lethal  2  in  one  X  and  the  genea 
for  bifid  and  tan  in  the  other.  The  stock  was  maintained  by  repeating  in 
each  generation  the  cross  of  wild-type  lethal-bearing  females  to  their  bifid- 
tan  brothers. 

Description. — The  gynandromorph  was  completely  bilateral,  the  left  side 
being  male  and  the  right  female.  The  left  side  showed  tan  body-color  through- 
out and  had  a  bifid  wing.  The  left  side  showed  all  the  size,  coloration,  and 
other  secondary  sexual  characters  of  the  male.  The  genitalia  were  male. 
Sections  showed  that  two  rudimentaiy  ovaries  were  present. 

Explanation. — A  non-cross-over  egg  containing  the  genes  for  lethal  2  was 
fertilized  by  an  X  sperm  with  the  genes  for  bifid  and  tan.     Elimination  of 


I 


38 


THE   ORIGIN   OF   GYNANDROMORPHS. 


one  of  the  maternal  lethal-bearing  X's  occurred  with  the  production  of 
bifid  tan  male  parts. 


bi 


hi 


t 


No.  1818.    July  4,  1915.     C.  B.  Bridges.    Text-figure  18  (diagram). 

Parentage. — One  X  chromosome  of  the  mother  carried  the  genes  for  sable 
and  for  forked;  the  other  was  wild-type.  The  X  chromosome  of  the  father 
carried  the  gene  for  forked. 

Description. — The  gynandromorph  was  completely  bilateral,  the  left  side 
being  male  and  the  right  female.  The  fly  was  not  forked  on  either  side. 
The  genitalia  were  female.     Sections  showed  ovaries  on  both  sides. 


Text-figure  17. 


Text-figure  18. 


Text-figure  19. 


Explanation. — An  egg  containing  the  normal  X  chromosome  was  fertilized 
by  the  forked  sperm.  A  paternal  X  suffered  elimination,  leaving  a  normal 
X  to  produce  the  male  side.  The  female  side  was  also  normal,  because  the 
maternal  X  present  carried  the  normal  allelomorph  of  forked. 

/ 


No.  T.     July,  1915.     E.  M.  Wallace.     Text-figure  19  (diagram). 

Parentage. — The  parentage  is  unrecorded,  but  from  the  characters  shown 
by  the  gynandromorph  it  is  probable  that  the  fly  came  from  notch  stock. 
The  mother  carried  the  dominant  gene  for  notch  wing  in  one  X  and  the  gene 
for  eosin  in  the  other.     The  father  was  eosin. 

Description. — The  right  side  was  male  with  a  sex-comb,  a  short  wild-tj^pe 
wing,  smaller  bristles,  smaller  half- thorax  and  half -abdomen.     The  tip  of 


THE   ORIGIN   OF   GYNANDROMORPHS. 


39 


the  abdomen  had  male  coloration  on  both  sides  and  the  genitalia  were  largely 
male.  The  right  eye  was  eosin  of  the  male  type.  The  left  side  was  mostly 
female  with  a  red  eye  and  a  large  notched  wing.  The  gonads  a.s  seen  through 
the  body-wall  seemed  to  be  both  ovaries. 

Explanation. — A  notch-bearing  egg   was  fertilized   by   an   eosin  sperm. 
Elimination  of  the  maternal  notch  X  occurred. 

N 


w' 


w 


Text-figure  20. 


No.  F.     January,  1916.     T.  H.  Morgan.     Text-figure  20  (diagram). 

Parentage. — The  parentage  of  gynandromorph  F  is  unrecorded,  though  it 
is  probable  that  it  was  found  in  a  wild  stock. 

Description. — The  fly  was  a  completely  bilateral  gynandromorph  having 
on  the  right  side  a  sex-comb,  shorter  wing,  shorter  bristles,  and  smaller  parts 
in  head,  thorax,  and  abdomen.  The  coloration  of  the  abdomen  was  male 
at  the  tip  on  the  right  side,  but  female  in  the  remainder.  The  genitalia  were 
entirely  female.  The  abdomen  contained  a  fully  developed  pair  of  ovaries 
and  she  produced  many  offspring  which  were  all  wild-type. 

Explanation. — Elimination  of  one  X  occurred  in  a  normal  female  zygote; 
whether  this  X  was  maternal  or  paternal  is  indeterminable. 


40 


THE    ORIGIN   OF   GYNANDROMORPHS. 


No.  380.     March  28,  1916.    A.  Weinstein.     No  diagram. 

Parentage. — The  mother  carried  the  genes  for  ruby  and  forked  in  one  X 
and  the  genes  for  eosin  and  sable  in  the  other  X.     The  father  was  eosin-bar. 

Description. — The  gynandro- 
morph  was  about  half  and  half, 
the  left  side  being  mainly  male 
and  the  right  female.  The  left 
side  of  the  head  and  thorax  and 
the  left  wing  were  smaller  and 
the  left  foreleg  bore  a  partly 
double  sex-comb.  The  left  eye 
was  eosin  bar  of  the  male  type. 
The  genitalia  were  double  pos- 
teriorly; there  was  a  penis  with 
claspers  and  anterior  to  the 
right  of  this  an  ovipositor  and 
female-type  anal  prominences. 
The  abdomen  was  female  in 
coloration,  except  at  the  tip  on 
the  left  side,  which  showed  the 
male  banding.  The  right  eye 
was  red  and  of  the  broad  hetero- 
zygous bar  female  type. 

Explanation. — A  ruby  forked 
X  egg  was  fertilized  by  an  eosin 
bar  X  sperm.  Elimination  of 
the  maternal  ruby  forked  X  oc- 
curred. 

r'  f 


Text-figure  21. 


W^ 


B 


We 


B 


No.  SS01122AAA7344512  Selection  Experiment.     January  18,  1917. 
T.  H.  Morgan,      Plate  4,  Figure  1  (diagram). 

Parentage. — The  mother  was  notch,  having  therefore  one  X  chromosome 
with  the  dominant  gene  for  notch;  the  other  X  carried  the  recessives  eosin 
and  ruby.     The  father  was  likewise  eosin  ruby. 

Description. — The  gynandromorph  was  male  on  the  right  side,  except  for 
spots  of  red  (female)  in  the  eosin  ruby  eye  of  that  side.  The  coloration  of 
the  abdomen  was  male  throughout.  The  genitalia  were  mainly  male,  but 
showed  female  parts.  The  left  side  was  mainly  female,  having  a  red  eye  and 
a  notch  wing  of  slight  type.  No  gonads  were  found  in  the  sections  examined, 
but  it  is  probable  that  there  were  very  rudimentary  ovaries. 

Explanation. — An  egg  bearing  the  gene  for  notch  was  fertilized  by  an 
X  sperm  with  the  genes  for  eosin  and  for  ruby.  Elimination  of  a  maternal 
X  chromosome  left  the  male  parts  to  be  determined  by  the  paternal  eosin 
ruby  X. 

N 


w" 


n 


w 


n 


PLATE  3 


jW*-^' 


#2* 


w-^ 


4 


la 


3.    Normal    $ 


v.*  -  •  ^'~- 


^  i 


'W 


3a.    Normal  f^ 


Sa?L 


r 


\ 


*UP' 


i;.   M.  Waulacic   I'inx 


GYNANDROMORPHS  OF  DROSOPHILA 


THE    ORIGIN   OF   GYNANDROMORPHS.  41 

No.  29.     February  11,  1918.     T.  H.  Morgan.     Text-figure  21  (drawing). 

Parentage. — Both  mother  and  father  were  eosin. 

Des(rription. — The  gynandromorph  was  bilateral,  ex(!ept  that  the  entire 
head  was  female,  having  eosin  eyes  of  the  dark  liomozygous  eosin  color. 
The  left  side  was  male,  having  a  sex-comb,  shorter  kigs,  shorter  bristles  and 
wing,  and  a  smaller  left  side  to  the  thorax  and  abdomen.  The  coloration 
of  the  abdomen  was  half  and  half,  but  there  appeared  to  be  a  pair  of  ovaries 
and  female  genitalia. 

Explanation. — An  egg  containing  an  X  chromosome  with  the  g(!ne  for 
eosin  was  fertilized  by  an  X  sperm  can-ying  eosin.  Elimination  of  either 
X  gave  the  nearly  bilateral  gynandromorph. 

w*  w' 


Gynandromorphs  Mainly  Female. 

No.  C2C19.     January    1914.     E.  M.  Wallace.     Plate  2,  Figure  3 

(colored  drawing). 

Parentage. — The  mother  was  white-eosin  compound,  having  the  genes  for 
yellow  and  white  in  one  X  and  eosin  in  the  other  X.     The  father  was  eosin. 

Description. — All  of  the  fly  was  gray  and  female,  except  the  upper  right 
half  of  the  thorax  and  the  right  wing,  which  were  yellow  and  male.  Both 
eyes  were  eosin,  of  the  dark  type  of  the  homozygous  eosin  female.  Well- 
developed  ovaries  were  present  on  both  sides.  Mated  to  a  yellow  white 
male  this  gynandromorph  was  fertile  and  produced  white-eosin  females  70; 
eosin  males  42;  yellow  white-eosin  females  53;  yellow  eosin  males  58. 

Explanation. — An  egg  with  a  cross-over  X  containing  the  genes  for  yellow 
and  eosin  was  fertilized  by  an  X  sperm  with  a  gene  for  eosin.  Elimination 
of  one  of  the  latter  left  the  maternal  X  to  produce  the  male  parts  on  the 
upper  right  side  of  the  thorax. 


to* 


No.  5137.    September  4,  1916.     C.  B.  Bridges.      Plate  2,  Figures  5  and  5a 

(colored  drawings). 

Parentage. — The  mother  had  one  chromosome  with  the  genes  for  vermilion, 
sable,  garnet,  and  forked,  and  the  other  X  with  the  genes  for  vermilion  and 
for  bar.  The  X-bearing  sperm  carried  the  genes  for  eosin  and  for  miniature 
wings. 

Description. — The  mosaic  was  entirely  female,  except  for  a  patch  of  eosin 
in  the  left  eye.  The  eosin  part  of  the  eye  was  round  and  light  eosin  (male 
type)  while  red  bar  both  above  and  below  (very  slight  amount  below).  The 
right  eye  was  red  bar.     The  whole  abdomen  was  full  of  eggs. 

Explanation. — An  egg  with  the  X  chromosome  carrying  the  genes  for 
vermilion  and  bar  was  fertihzed  by  a  sperm  carrying  the  genes  for  eosin  and 
miniature.     Elimination  of  a  maternal  chromosome  took  place,  leaving  the 


42 


THE   ORIGIN   OF   GYNANDROMORPHS. 


one  X  with  eosin  and  miniature  genes  to  produce  the  male  parts,  which  in 
this  case  affected  visibly  only  a  part  of  the  left  eye. 


w^ 


in 


w" 


in 


No.  M,  114.    January  23,  1914.     C.  B.  Bridges.     Text-figure  22   (diagram). 

Parentage. — One  of  the  X  chromosomes  of  the  mother  contained  the  gene 
for  eosin,  the  other  the  gene  for  bar.     The  father  was  white  bar.     Both 
parents  were  heterozygous  for  the  autosomal  recessive 
gene  "whiting,"  which  is  a  specific  modifier  of  eosin. 

Description. — The  gynandromorph  was  somewhat 
more  than  half  female.  The  left  side  of  the  gynan- 
dromorph, except  for  the  head,  was  male,  with  sex- 
comb,  smaller  bristles  half-thorax  and  wing.  In  col- 
oration the  abdomen  was  male  on  the  left  and  female 
on  the  right.  The  genitalia  were  entirely  female. 
The  head  had  heterozygous  bar  (female)  eyes,  which 
were  white-eosin  compound  (female)  in  color.  A  pair 
of  ovaries  was  present. 

Explanation. — An  egg  containing  the  X  chromo- 
some with  the  gene  for  eosin  was  fertilized  by  the 
X  sperm  with  the  genes  for  white  and  for  bar. 
Either  chromosome  may  have  been  the  one  to  suffer 
elimination;  which  one  it  was  could  not  be  determined, 
since  the  head  did  not  show  male  parts. 


No.  438.    August  16,  1914.     C.  B.  Bridges. 

figure  23  (diagram). 


Text- 


Text-fiqure  22. 

The  X  chromosome  of 


Text-figure  23. 
W 


Parentage. — One  X  chro- 
mosome of  the  mother  con- 
tained the  genes  for  eosin 
and  for  vermilion,  the  other 
X  the  gene  for  white  eyes, 
the  male  carried  the  gene  for  eosin. 

Description. — The  left  side  of  the  gynandromorph 
was  largely  male  with  a  white  eye  (containing  a 
fleck  of  white-eosin),  a  sex-comb,  and  a  shorter  wing. 
The  right  side  was  female,  with  a  white-eosin  com- 
pound eye,  no  sex-comb,  and  a  longer  wing.  The 
abdomen  was  banded  like  a  female.  When  bred  as 
a  female  the  fly  gave  the  classes  expected  for  a 
white-eosin  compound.     No  sections  were  made. 

Explanation. — An  egg  containing  the  X  chromo- 
some with  the  gene  for  white  was  fertilized  by  an  X 
sperm  carrying  the  gene  for  eosin.  The  latter — the 
paternal  chromosome — suffered  elimination,  leaving 
the  white-bearing  X  to  produce  the  male  side. 
The  color  of  the  eye  on  the  female  side  was  white-eosin 
compound,  which  is  the  expected  result  for  the  two 
X's  involved. 


?/' 


W 


THE    ORIGIN    OF   GYNANDROMORPHS. 


43 


No.  922.    December  16, 1914.    C.  B.  Bridges.    Text- 
figure  24  (diagram). 

Parentage. — One  of  the  X  chromosomes  of  the 
mother  contained  the  genes  for  eosin  and  for  vermil- 
ion, the  other  X  the  gene  for  forked.  The  X  chromo- 
some of  the  male  carried  the  genes  for  white  and  for 
bar. 

Description. — The  fly  was  female  throughout  (with- 
out sex-combs)  and  possessed  white-eosin  heterozy- 
gous-bar eyes,  except  that  the  tip  of  the  abdomen 
on  the  left  side  was  banded  like  a  male.  Below  there 
was  a  normal  penis  and  male  armature.  In  sec- 
tions an  ovary  was  found  on  one  side,  nothing  on 
the  other. 

Explanation. — An  egg  containing  the  X  chromo- 
some with  the  genes  for  eosin  and  for  vermilion  was 
fertilized  by  the  X-bearing  sperm  with  the  genes  for 
white  and  for  bar.  Elimination  of  either  X  chro- 
mosome would  account  for  the  male  parts  at  the  tip 
of  the  abdomen. 


vf 


V 

t 


w^ 


Text-figure  24. 


or 


w 


B 


w 


B 


No.  925.     December  18,  1914.      C.  B.  Bridges.      Text-figure  25  (diagram). 

Parentage. — The  mother  was  club,  carrying  in  one  X  the  sex-linked  gene 
club,  and  in  the  other  X  lethal  2  which  is  a  deficiency  for  club.  The  X  sperm 
of  the  father  carried  the  genes  for  eosin  and  for  miniature. 

Description. — The  only  male  part  was  the  right  eye,  which  was  eosin  (male 
type)  in  color,  except  for  a  fleck  of  red  (female).  The  fly  was  fertile  as  a 
female  when  mated  to  a  wild  male  and  produced:  No.  1117;  wild  type  females, 
101;  eosin  miniature  males,  55;  miniature  male,  1;  eosin  males,  9. 

Explanation. — An  egg  with  an  X  bearing  the  gene  for  lethal  2  was  fertilized 
by  an  X  sperm  with  the  genes  for  eosin  and  miniature.  Elimination  took 
place  in  one  of  the  maternal  chromosomes,  leaving  the  paternal  X  with  eosin 
and  miniature  to  form  the  male  parts,  viz,  the  right  side  of  the  head  (in  part). 
The  rest  of  the  mosaic  was  female;  hence  both  wings  were  wild-type. 

Cl 


w 


—r- 
m 


w^ 


m 


No.  1010.     December  20,  1914.     C.  B.  Bridges.     Text-figure  26  (diagram). 

Parentage. — One  X  chromosome  of  the  mother  carried  the  genes  for  yellow 
and  for  white,  and  the  other  X  the  gene  for  lethal  6.  The  X  chromosome  of 
the  father  carried  only  wild-type  genes. 


44 


THE    ORIGIN   OF   GYNANDROMORPHS. 


Description. — The  left  side  of  the  thorax  of  the  gynandromorph  was  male, 
with  a  sex-comb  and  a  shorter  wing.  Both  eyes  were  red  and  female.  The 
abdomen  and  genitalia  were  female.  The  body-color  was  wild-type  through- 
out.    Sections  showed  ovaries  on  both  sides. 

Explanation. — An  egg  containing  the  lethal  6  X  chromosome  was  fertilized 
by  a  wild-type  X  sperm.  Either  one  of  the  X  chromosomes  being  eliminated 
would  account  for  the  result.  If  the  paternal  X  were  eliminated  the  male 
parts  would  be  lethal  6,  and  hence  it  is  more  probable  that  the  maternal  X 
was  eliminated. 


/. 


I, 


or 


No.  1808.     July  7,  1915.     C.  B.  Bridges.     Text-figure  27  (diagram). 

Parentage. — The  mother  was  pure  for  the  second-chromosome  recessives 
purple,  curved,  and  speck.  The  father  was  heterozygous  for  the  dominant 
star  (eyes).     No  sex-linked  mutant  characters  were  present. 


Text-figure  25. 


Text-figure  26. 


Text-figure  27. 


Text-figure  28. 


Description. — The  gynandromorph  was  female  throughout,  except  for  the 
abdomen,  which  had  male  coloration  on  the  left  side  and  was  twisted  to  the 
left.  A  perfect  penis  was  present.  The  eyes  were  star.  The  male  parts 
could  not  have  shown  the  recessive  second-chromosome  characters,  even 
had  they  been  present.  No  testes  or  ovaries  were  found,  but  there  was  a 
genital  tube  with  pointed  cells  like  abnormal  spermatozoa. 


THE    ORIGIN   OF   GYNANDROMORPHS.  45 

No.  5238.     September  23,  1916.     C.  B.  Bridges.     Text-figure  28  (diiigram). 

Parentage. — One  of  the  X  chromosomes  of  the  mother  carried  the  genes 
for  vermihon  eye-color  and  for  bar  eye,  the  other  X  the  gene  for  forked 
bristles.  The  X  chromosome  of  the  father  carried  the  genes  for  eosiii, 
vermilion,  and  forked. 

Description. — The  fly  was  mainly  female,  but  is  exceptionally  interesting 
from  the  peculiar  description  of  the  male  parts,  which  constitute  a  v(;ry 
narrow  stripe  running  through  the  middle  of  the  left  eye  and  along  the  left 
side  of  the  thorax,  including  the  wing.  The  left  eye  was  eosin  vermilion  in 
color  in  the  male  parts  and  red  in  the  female  parts,  both  above  and  below  the 
eosin  vermilion.  These  female  parts  were  heterozygous  for  bar  and  the  red 
portions  above  and  below  were  therefore  characteristically  narrow,  while  the 
eosin-vermilion  part  was  not-bar  and  projected  forward,  so  that  the  male 
stripe  could  be  traced  forward  to  the  normal  margin  of  the  round  eye.  The 
male  part  of  the  thorax  could  likewise  be  traced  by  means  of  the  forked 
bristles,  of  which  there  were  three  anterior  to  the  wing,  one  above,  and  none 
below.  The  wing  itself  was  included  in  the  male  region  and  was  smaller 
and  had  forked  marginal  bristles.     There  was  no  sex-comb  on  the  left  side. 

Explanation. — An  egg  containing  an  X  chromosome  with  the  gene  for  bar 
was  fertilized  by  the  eosin  vermilion  forked  sperm.  A  maternal  X  suffered 
elimination,  leaving  the  eosin  vermilion  forked  X  to  produce  the  male  parts. 

B 


W^  V  f  W  V  f 

No.  2.     September,  1917.     T.  H.  Morgan.     Text-figure  29  (drawing). 

Parentage. — The  fly  appeared  in  "selected  notch"  stock  in  which,  in  each 
generation,  red-eyed  notch  females  were  bred  to  eosin  ruby 
males. 

Description. — The  right  eye  was  red,  the  left  partly  red, 
partly  eosin  ruby,  with  a  very  irregular  boundary-line;  other- 
wise the  fly  was  female. 

Explanation. — An  egg  with  a  gene  for  notch  wing  was  fer- 
tilized  by  an  X  sperm  bearing  eosin  and  ruby.  Elimination 
of  one  of  the  maternal  X's  left  a  part  of  one  side  of  the  head 
with  the  eosin  ruby  X.  The  wings,  although  not  showing 
notch,  must  have  contained  the  gene.  Since  less  than  half  text-fioure  29. 
of  the  notch  flies  in  this  selected  stock  showed  the  notch 
character,  its  absence  here  is  not  diflficult  to  explain. 


W       Vb  W'       rb 

No.  477.     October  31,  1917.     D.  E.  Lancefield.     Text-figure  30  (drawing). 

Parentage. — One  of  the  X  chromosomes  of  the  mother  had  a  bar  gene, 
the  other  a  gene  for  forked.     The  father  was  bar. 

Description. — The  head  was  small,  with  round  eyes  and  forked  bristles. 
The  thorax  and  wings  seemed  to  be  female.  No  sex-combs  present.  The 
abdomen  was  entirely  female,  with  eggs  inside,  but  she  did  not  breed. 


46 


THE   ORIGIN   OF   GYNANDROMORPHS. 


Explanation. — An  egg  containing  an  X  with  a  gene  for  forked  was  fertilized 
by  a  bar  X  sperm.  The  paternal  X  with  bar  was  eliminated,  leaving  the 
head  male  and  forked. 


/ 


/ 


Text-figure  30. 

No.   71.     October  23,    1917.     E.   M.   Wallace.     Text-figure  31    (drawing). 

Parentage. — Pure  stock  of  bar. 

Description. — A  female  was  observed  that  had  a  short  left  wing.  Closer  ex- 
amination showed  that  the  bristles  on  that  side  of  the  thorax  and  head  were 
shorter  and  that  the  left  side  of  the  head  was  sUghtly  contracted  and  the  eye 
smaller.     It  is  probable  that  the  left  side  of  head  and  thorax  (dorsally)  were  male. 

No.  7530.     August  18,  1917.     C.  B.  Bridges.     Text-figure  32  (diagram). 

Parentage. — One  of  the  X  chromosomes  of  the  mother  carried  the  gene  for 
facet  eye  and  the  other  X  the  gene  for  notch  wings  (dominant).  The  X 
chromosome  of  the  father  carried  the  gene  for  facet. 

Description. — The  left  side  of  the  gynandromorph  was  male,  with  a  shorter 
wing,  sex-comb,  and  smaller  eye,  whose  markedly  faceted  eye  was  character- 
istic for  that  character  as  it  appears  in  the  male  of  the  mutant  type.  The 
female  side  had  a  faceted  eye  of  the  female  type,  which  is  far  less  marked. 
The  abdomen  was  banded  as  in  the  female,  but  below  a  penis  was  present. 
Testes  were  found  on  both  sides,  with  an  abundance  of  sperm. 

Explanation. — An  X  egg-carrying  facet  was  fertiUzed  by  the  X  sperm- 
carrying  facet.  Elimination  of  either  occurred.  The  gonads  were  formed 
from  a  male  cell.  Very  frequently  a  male-appearing  abdomen  contains 
ovaries;  only  very  rarely  does  a  female-type  abdomen  contain  testes. 


THE    ORIGIN    OF   GYNANDROMORPHS. 


47 


No.  Xi.     January,  1914.     E.  M.  Wallace.     No  diagram. 

Parentage. — This  gynandromorph  arose  in  a  mass-culture  whose  parents 
were  yellow  white  females  and  eosin  males. 

Description.— The  gynandromorph  was  largely  female.  The  male  parts 
were  yellow  and  included  the  left  dorsal  side  of  the  thorax  with  the  shorter 
wing  and  the  left  side  of  the  abdomen.     These  parts  were  all  smaller,  bore 


Text-figure  31. 


Text-figure  32. 


smaller  bristles,  and  the  left  half  of  the  abdomen  had  male-type  coloration. 
The  genitalia  were  female.  The  female  parts  throughout  were  wild-type  in 
body-color,  including  especially  the  left  legs  and  all  the  head.  There  were 
no  sex-combs.     The  eyes  were  both  white-eosin  compound. 

Explanation. — A  yellow  white  X  egg  was  fertilized  by  an  eosin  X  sperm. 
Elimination  of  the  paternal  X  occurred. 


y    w 


y    w 


w^ 


48  THE    ORIGIN   OF   GYNANDROMORPHS. 

Gynandromorphs  Mainly  Male. 

No.  GiAboCaz.     March,  1914.     E.  M.  Wallace.     Plate  2,  figures  6  and  6a 

(colored  drawings). 

Parentage. — The  mother  was  a  yellow  white  female,  a  daughter  of  gynandro- 
morph  GiAb2C.  The  father  was  an  ebony  (third-chromosome)  male.  This 
mating  was  part  of  the  second  of  the  tests  specifically  designed  to  show 
the  absence  of  elimination  of  autosomes  in  the  production  of  gynandromorphs. 

Description. — The  gynandromorph  was  mainly  male,  with  only  the  head 
and  genitaha  female.  The  color  of  the  entire  thorax,  abdomen,  legs,  and 
wings  was  yellow,  and  correspondingly  the  bristles  of  these  parts  were  brown. 
These  yellow  parts  were  male,  as  proved  by  the  sex-combs  on  both  forelegs, 
by  the  small  (male)  size  of  the  bristles,  of  the  thorax,  and  particularly  of  the 
abdomen,  and  by  the  male  coloration  and  shape  of  the  abdomen.  However, 
the  genitalia  were  an  exception,  for  the  anal  prominence  and  the  ovipositor 
were  purely  female  in  structure  and  bore  black  spines  which  showed  that  the 
body-color  was  wild-type.  The  head  was  entirely  female,  as  proved  by  its 
large  size,  the  wild-type  color  with  black  bristles,  and  by  the  red  eyes.  Thus 
the  head  and  genitalia — the  two  ends  of  the  fly — were  female  and  all  the 
region  between  was  male. 

Explanation. — An  egg  carrying  the  genes  for  yellow  and  white  was  fertilized 
by  sperm  carrying  only  wild-t>T)e  genes  in  the  X.  EUmination  of  a  paternal 
X  occurred  and  subsequent  shifting  isolated  a  female  cell  which  gave  rise  to 
the  genitalia.  The  absence  of  ebony  proves  that  the  third  chromosome  did 
not  undergo  elimination. 


y    w  y    w 

No.  X2.     February  1914.     E.  M.  Wallace.     Text-figure  33  (drawing). 

Parentage. — Gynandromorph  X2  appeared  in  a  mass-culture,  the  mothers 
of  which  carried  yellow  and  white  in  oneX  and  eosin  in  the  other;  the  fathers 
were  yellow- white. 

Description. — The  gynandromorph  was  mainly  male.  The  female  parts 
were  confined  to  the  abdomen,  which  had  female  coloration  on  the  left  side 
and  apparently  male  on  the  right.  The  abdomen  was  twisted  to  the  right, 
which  also  suggests  that  the  right  side 
was  male.  However,  the  genitalia  re- 
versed this  relation,  the  right  side 
being  largely  female,  with  an  anal 
prominence  of  female  type;  the  left 
side  was  male  and  there  was  a  median 
penis.  The  abdomen  was  of  large  size 
and  a  pair  of  ovaries  could  be  clearly 
seen  within.  The  thorax  and  head  were 
entirely  male,  as  evidenced  by  their  size 
and  the  type  of  bristles  and  the  pres- 
ence of  sex-combs  on  both  forelegs. 
The  eyes  were  both  white  and  the  body-  Text-figure  33. 

color  was  yellow  throughout. 

Explanation. — A  yellow  white  X  egg  was  fertilized  by  a  yellow  white  X 
sperm.  EUmination  of  either  X  occurred.  An  alternative  explanation  is 
that  the  egg  was  fertilized  by  a  Y  sperm  giving  a  yellow  white  male.  Somatic 
non-disjunction  resulted  in  a  cell  with  both  daughter  X's  present,  and  this 
gave  rise  to  the  female  parts. 


THE   ORIGIN   OF   GYNANDROMORPHS. 


49 


No.  3.     February  1915.     T.  H.  Morgan.     Text-figure  34  (drawing) 

Parentage. — The  mother  was  rudimentary  and  the  father  bar. 

Description. — The  gynandromorph  was  about  three-fourths  male.  The 
right  halves  of  the  head  and  of  the  thorax  were  female,  being  larger  in  size, 
having  larger  bristles  and  a  larger  wing,  which  was  wild-type,  and  no  sex- 
comb.  The  right  eye  was  heterozygous  bar  (female).  The  left  eye  was  bar 
of  the  male  type  and  the  left  halves  of  the  head  and  of  the  thorax  were  male. 
The  left  wing  was  smaller,  but  not  inidimentary.  The  abdomen  seemed  en- 
tirely male,  with  a  normal  penis.  This  gynandromorph  was  tested  as  to 
sexual  behavior  and  was  found  to  pay  no  attention  to  mature  virgin  females. 
An  account  of  this  gynandromorph  and  the  drawing  have  been  previously 
published.     (Morgan,  Am.  Nat.,  V.  49,  p.  240,  April  1915.) 

Explanations. — An  egg  with  a  rudimentary  X  was  fertilized  by  an  X  sperm 
carrying  bar.  Elimination  of  the  maternal  rudimentary  X  occurred.  Some 
of  the  female  'cells  were  lost  in  cleavage,  so  that  the  individual  is  prepon- 
derantly male. 


Text-figure  34. 


Text-figure  35. 


No.  2317.     November  2,  1915.     C.  B.  Bridges.     Text-figure  35  (drawing). 

Parentage. — One  X  chromosome  of  the  mother  carried  the  genes  for  rudimen- 
tary wing  and  fused  veins,  and  the  other  X  the  gene  for  bar.  The  X  chromo- 
some of  the  father  carried  the  genes  for  vermilion  eye  and  forked  bristles. 

Description. — The  left  side  of  the  gynandromorph  is  male,  with  sex-comb 
and  rudimentary  fused  wing,  the  left  side  of  the  abdomen  is  male,  but  the 
genitalia  are  female.  The  ocelli  on  the  head  are  like  those  of  fused,  and  the 
head  is  therefore  male.     No  sections  were  made. 


50 


THE    ORIGIN   OF   GYNANDROMORPHS. 


Explanations. — An  egg  containing  the  rudimentary  fused  X  was  fertilized 
by  the  vermiHon  forked  sperm.  A  paternal  vermilion  forked  X  was  elim- 
inated, leaving  the  other  rudimentary  fused  X  to  produce  the  male  side, 
while  the  female  side  contains  both  original  X's,  namely,  rudimentary  fused 
and  vermilion  forked,  and  is  accordingly  wild-type. 


A 


/. 


V  f 

No.  3272.     February  10,  1916.     C.  B.  Bridges.     Text-figures  36  and  36a 

(drawings). 

Parentage. — One  X  chromosome  of  the  mother  carried  the  genes  for  sable, 
garnet  and  also  "sable-duplication"  at  zero.  The  other  X  carried  the  genes 
for  eosin  and  for  miniature.     The  father  was  eosin-miniature. 

Descriptions. — The  entire  abdomen  was  apparently  male  in  shape,  banding, 
and  genitalia,  though  it  is  not  known  whether  testes  or  ovaries  were  present. 
The  right  side  of  the  thorax  was  smaller  in  size  and  bore  smaller  bristles  and 


Text-figuhe  36o. 


Text-figure  36. 


Text-figure  37. 


a  smaller  (male-type)  miniature  wing.  All  right  legs  were  male  and  both  fore- 
legs bore  sex-combs.  The  right  eye  (see  drawing)  had  a  streak  of  male 
tissue  ("light"  eosin  color)  running  forward  completely  through.  Above  and 
below  this  streak  the  tissue  was  female  ("dark"  eosin  color)  There  is  one 
other  curious  feature — the  left  foreleg  as  well  as  the  right  bore  a  sex- comb. 
The  head,  except  the  male  streak,  the  right  side  of  the  thorax  with  its  miniature 
wing,  and  the  two  rear  legs  were  female 

Explanations  — An  egg  bearing  the  eosin  miniature  non-cross-over  X  was 
fertilized  by  the  X  sperm  carrying  eosin  and  miniature  Elimination  of  one 
of  these  X's  (either  maternal  or  paternal)  was  followed  by  shifting  of  cleavage 
nuclei  or  by  shifting  of  the  anlage  in  the  formation  of  the  pupa. 


THE   ORIGIN    OF   GYNANDROMORPHS. 


51 


Gynandromorphs  Roughly  "Fore-and-Aft." 
No.  II 139.     January  12,  1914.     C.  B.  Bridges.     Text-figure  37  (diagram). 

Parentage. — The  mother  was  black  (second  chromosome),  but  carried  only 
wild-type  genes  in  her  X  chromosomes.     The  father  was  a  bar  not-])Iack  male. 

Descriptions. — The  fly  was  heterozygous  bar  in  both  eyes  and  female  through- 
out, except  for  the  external  genitalia,  which  were  male  (penis),  and  the 
coloration  of  abdomen.      Sections  showed  that  a  pair  of  ovaries  was  present. 

Explanations. — An  egg  with  a  wild-type  X  was  fertilized  by  the  X  sperm 
with  the  gene  for  bar.  Since  the  male  parts  did  not  involve  the  eye,  it  can 
not  be  determined  whether  they  arose  from  cells  carrying  the  bar  (paternal) 
or  the  wild-tj^e  (maternal)  X.  The  fly  did  not  show  black  in  the  male  parts, 
but  since  the  male  region  was  so  small  and  also  normally  dark-colored,  this 
case  could  not  be  accepted  as  proving  that  the  elimination  did  not  aff"ect  the 
autosomes,  as  is  proved  in  several  later  cases,  especially  devised  for  that  purpose. 


or 


B  B 

No.  1813.     July  5,  1915.     C.  B.  Bridges.     Text-figure  38  (diagram). 

Parentage. — One  X  chromosome  of  mother  carried  the  genes  for  forked  and 
for  cleft  (wing);  the  other  X  only  wild-type  genes.     The  father  was  forked. 

Descriptions. — The  head,  thorax,  wings,  and  legs  were  female.  The  ab- 
domen had  the  male  coloration  and  a  normal  penis.     The  (poor)  sections 


Text-figure  38. 


Text-figure  39. 


Text-figure  40. 


showed  that  at  least  one  ovary  was  present.     The  wings  were  not  cleft  and 
the  male  parts  showed  no  forked  spines. 

Explanations.— The  egg  contained  the  wild-type  X  and  was  fertilizec  by  the 
X  sperm  carrying  forked.  The  paternal  X  was  eliminated,  leaving  the  male 
parts  wild-type.  e 


52  THE   ORIGIN   OF   GYNANDROMORPHS. 

No.  2204.     October  5,  1914.     C.  B.  Bridges.     Text-figure  39  (diagram). 

Parentage. — One  X  of  the  mother  carried  the  gene  for  eosin,  the  other  the 
genes  for  vermihon  and  forked.     The  father  was  bar. 

Description. — The  gynandromorph  was  of  the  "fore-and-aft"  type.  The 
abdomen  was  of  the  male  shape,  with  male  coloration  on  the  left  side  and 
partially  male  on  the  right.  There  was  a  normal  penis.  The  eyes  were 
heterozygous  bar  (female)  and  the  head,  thorax,  legs,  and  wing  were  female. 
Sections  showed  that  email  ovaries  were  present. 

Explanations. — Since  the  male  parts  were  not  forked,  the  egg  probably 
carried  the  eosin  X.  The  X  sperm  carried  bar.  The  eyes  were  female  and 
there  is  no  criterion  as  to  which  X  was  eliminated.  An  alternative  explana- 
tion assumes  a  vermihon  forked  X  in  the  egg,  and  subsequent  elimination  of 
this  same  X  to  give  the  not-forked  male  parts. 

No.  X.  August  1916.   A.  Weinstein.    Text-figure  40  (drawings  of  wings) . 

Parentage. — The  mother  had  the  genes  for  eosin,  ruby,  and  forked  in  one 
X  and  for  fused  in  the  other.     The  father  was  probably  eosin  ruby  forked. 

Description. — The  gynandromorph  was  largely  male  anteriorly  and  female 
posteriorly.  The  head  was  entirely  male,  with  eosin  ruby  eyes.  There 
were  sex-combs  on  both  forelegs,  which  means  that  the  ventral  part  of  the 
thorax  was  male.  The  left  dorsal  part  was  also  male,  having  a  small  wing 
which  was  fused.  The  right  dorsal  part  was  female  with  a  large  wild-type 
wing.     The  abdomen  and  genitalia  were  female. 

Explanations. — The  egg  carried  a  cross-over  eosin  ruby  fused  X  and  the 
sperm  an  eosin  ruby  forked  X.     Elimination  of  the  paternal  X  occurred. 

W      rb  fu  W     rb  fu 


w"     rtj  j 

No.  4614.     January  22,  1918.     A.  H.  Sturtevant.     Text-figure  41  (diagram). 

Parentage. — One  X  of  the  mother  carried  the  genes  for  eosin,  vermilion, 
and  forked;  the  other  X  carried  only  wild-type  genes.  One  of  the  third- 
chromosomes  carried  the  recessive  genes  for  sepia,  spineless,  kidney,  sooty, 
and  rough;  the  other  was  wild-type.     The  father  was  a  bar  male  from  stock. 

Description. — Except  for  the  wings,  the  gynandromorph  is  divided  antero- 
posteriorly.  The  right  wing  was  slightly  larger  than  the  left  and  may  have 
been  female.  The  other  wing  and  the  remainder  of  the  thorax  was  male. 
There  were  sex-combs  on  both  forelegs.  The  head  was  entirely  male,  with 
eosin-vermilion  eyes  and  forked  bristles.  The  thorax  and  legs  had  also  forked 
bristles.  The  abdomen  was  female,  both  in  banding  and  in  shape.  The 
genitalia  were  female,  but  slightly  abnormal.  Tested  as  a  female  she  proved 
sterile.  None  of  the  third-chromosome  recessives  showed  in  any  part,  either 
male  or  female,  of  the  gynandromorphs. 

Explanations. — An  egg  containing  the  non-cross-over  eosin  vermilion  forked 
X  was  fertilized  by  an  X  sperm  carrying  bar.  The  paternal  X  was  eliminated, 
producing  the  anterior  male  parts.  The  absence  of  the  recessive  third-chromo- 
some characters  in  the  male  parts  proves  that  the  elimination  of  the  X  was 
independent  of  the  third  chromosome. 

w^  V  f  vf  V  f 

I  I  I  I  t  I 

B 


THE    ORIGIN   OF   GYNANDROMORPHS. 


53 


Gynandromorphs  Produced  by  XXY  Females. 

No.  N  2.     December  12,  1912.     C.  B.  Bridges.     Plate  3,  Figures  1  and  la 

(colored  drawings) . 

Parentage. — The  mother  was  an  XXY  female  homozygous  for  wliite  and 
heterozygous  for  the  third-chromosome  mutant  pink.  The  father  was  red- 
eyed,  and  also  heterozygous  for  pink.  Both  parents  were  exceptions  produced 
by  secondary  non-disjunction. 

Description. — The  fly  was  a  completely  bilateral  gynandromorph,  male 
on  left  side,  female  on  right.  The  male  side  was  smaller,  with  sex-comb, 
the  genitalia  half  and  half.     The  fly  was  unable  to  breed  as  a  male  or  as  a 


Text-figure  41. 


Text-figure  42. 


Text-figure  43. 


Text-figure  44. 


female.  The  abdomen  was  large  and  evidently  contained  a  pair  of  ovaries 
The  fly  was  figured  in  Heredity  and  Sex,  page  163,  and  the  origin  given  in 
Journ.  Exp.  Zool.,  1913,  page  597. 

Explanations. — A  regular  X  egg  carrying  the  gene  for  white  was  fertilized 
by  an  X  sperm  carrying  the  wild-type  allelomorph  red.  One  of  the  maternal 
X's,  bearing  the  gene  for  white  eye,  was  eliminated.  The  white-eye  character 
therefore  does  not  appear  on  either  side.  As  both  parents  were  heterozygous 
for  pink,  the  fly  may  have  come  from  third  chromosomes  bearing  normal 
genes  only,  or  one  of  them  may  have  had  the  gene  for  pink,  so  that  the  g>'nan- 
dromorph  is  heterozygous. 

w 


No.  N  3.     November  30,  1912.     C.  B.  Bridges.     Plate  3,  Figures  2  and  2a 

(colored  drawings),     (See  fig.  17.) 

Parentage. — The  mother  was  an  XXY  female,  carrj'ing  white  in  both  X 
chromosomes.     The  father  was  a  wild  male. 


54  THE    ORIGIN   OF   GYNANDROMORPHS. 

Description. — The  gynandromorph  was  entirely  female,  except  for  the  tip 
of  the  abdomen  below,  where  a  perfectly  normal  penis  and  male  genitalia  were 
found.  The  anal  prominence  and  the  parts  immediately  surrounding  the 
genitalia  were  also  male.  The  posterior  ventral  plate  was  male  type,  being 
broad,  rounded,  and  hairless. 

No.  1221.     February  2,  1915.     C.  B.  Bridges.     Text-figure  42  (diagram). 

Parentage. — The  mother  was  an  XXY  wild-type  female,  one  of  whose  X 
chromosomes  carried  the  gene  for  eosin,  the  other  X  only  wild-type  genes. 
The  father  was  bar. 

Description. — The  gynandromorph  was  bilateral,  except  for  the  head, 
which  was  entirely  female,  with  red  bar  eyes  of  the  heterozygous  type.  The 
right  side  of  the  thorax  dorsally  was  male,  with  shorter  bristles  and  very  small 
wing  (abnormal).  There  were  no  sex-combs.  The  right  side  of  the  abdomen 
was  male  in  coloration,  and  the  genitalia  were  almost  entirely  male.  There 
was  a  pair  of  testes  with  ripe  spermatozoa.  The  two  halves  of  the  thorax 
failed  to  come  together  and  the  male  and  female  parts  were  unfused. 

Explanations. — The  egg  carried  the  eosin  X  and  may  or  may  not  have  con- 
tained a  Y.  The  sperm  was  the  X  sperm  carrying  bar.  Elimination  of  either 
X  occurred.  It  is  possible  that  the  spina  bifida  condition  may  have  been  a 
result  of  the  gynandromorphism. 

No.  1892.     July  19,  1915.     C.  B.  Bridges.     Text-figure  43  (diagram). 

Parentage. — The  mother  was  a  wild-type  XXY  female,  which  was  an  ex- 
ception from  "high"  non-disjunction.  One  X  carried  the  gene  for  eosin,  the 
other  the  genes  for  vermilion  and  forked.     The  father  was  bar. 

Description. — The  fly  was  female  throughout,  except  that  the  left  side  of  the 
abdomen,  especially  at  the  tip,  showed  male  coloration  and  the  genitalia 
were  entirely  male.     The  eyes  were  heterozygous  bar  (female). 

Explanation. — An  egg  with  one  X  (either)  and  with  or  without  a  Y  (even 
chance)  was  fertilized  by  an  X  sperm  carrying  the  gene  for  bar.  Elimination 
of  either  X  occurred. 

No.  7673.     October  16,  1917.     C.  B.  Bridges.     Plate  4,  Figure  3  (drawing). 

Parentage. — The  mother  was  an  eosin-eyed  XXY  exception  from  a  special 
sttain  of  "high"  non-disjunction  (He),  which  had  arisen  by  equational  non- 
disjunction from  the  regular  high  gtj-ain.  One  of  her  X  chromosomes  carried 
the  gene  for  eosin  and  the  other  the  genes  for  eosin  and  forked.  The  father 
was  bar. 

Description. — The  male  parts  of  the  gynandromorph  constituted  the  entire 
head,  which  had  eosin  eyes  of  the  male  type  and  forked  bristles;  the  left 
side  of  the  thorax,  which  had  forked  bristles,  was  smaller,  with  a  male-size 
wing  and  a  sex- comb  and  a  slight  patch  of  male  tissue  at  the  tip  of  the  ab- 
domen, but  on  the  right  side,  not  the  left.  The  abdomen  was  twisted,  as  it 
usually  is  when  bilateral,  but  since  the  bristles  were  not  forked,  the  male 
parts,  if  any,  must  have  been  below  or  internal.     The  right  wing  was  abnormal. 

Explanations. — An  X  egg  carrying  the  genes  for  eosin  and  forked  was  fertil- 
ized by  the  X  sperm  carrying  the  gene  for  bar.  Whether  or  not  a  Y  was 
present  in  the  egg  is  not  known  (chances  even) .  Elimination  of  a  paternal 
bar  X  occurred. 

iv^  f  to'  f 

I  ■  I  I 

B 


KLAIL  4 


GYNANDROMORPHS  OF  DROSOPHILA 


THE   ORIGIN    OF   GYNANDROMORPHS.  55 

No.  5485.     October  18,  1916.     C.  B.  Bridges.     Text-figure  44  (diagram). 

Parentage. — The  mother  was  an  XXY  female,  one  of  whose  chromosomes 
contained  the  genes  for  yellow  and  for  white,  the  other  X  the  gene  for  lethal  7. 
The  X  chromosome  of  the  father  carried  the  genes  for  yellow,  claret,  vermilion, 
and  forked. 

Description. — The  gynandromoi-ph  was  a  yellow  female,  except  that  three- 
quarters  of  the  right  eye  was  white  in  color  and  male,  the  remainder,  which 
was  a  perfect  quarter  sector  of  the  eye,  being  red  and  female.  Sections 
showed  normal  ovaries  to  be  present. 

Explanations. — An  egg  containing  the  X  chromosome  with  the  genes  for 
yellow  and  for  white  was  fertihzed  by  the  X  sperm  with  the  genes  for  yellow 
and  the  three  other  recessive  genes  named  above.  Elimination  of  a  paternal 
chromosome  occurred,  leaving  the  yellow  white  X  to  determine  the  character  of 
the  male  parts,  viz,  the  right  eye,  except  for  a  triangular  area  of  female  tissue. 

y        rf  V  f 


y  w  y    w 

Gynandromorphs  of  Complex  Type. 
No.  487.     November  27,  1917.     D.  E.  Lancefield.     Text-figure  45  (drawing). 

Parentage. — The  mother  was  an  XXY  female  homozygous  for  eosin  and 
miniature.     The  father  was  a  wild  male. 

Description. — The  distribution  of  male  and  female  parts  was  very  complex. 
The  entire  head  was  female,  as  evidenced  by  its  large  size  and  by  the  color 
of  both  eyes,  which  was  eosin  of  the  dark  female  type.  The  right  dorsal  part 
of  the  thorax  was  female,  as  shown  by  its  large  size  and  the  large  size  of 
the  bristles  and  of  the  wing,  which  was  also  wild-type  and  not  miniature. 
The  only  other  female  parts  seemed  to  be  the  left  ventral  part  of  the  thorax, 
including  left  legs,  since  left  foreleg  carried  no  sex-comb.  The  other  two 
sectors  of  the  thorax — the  right  ventral  and  the  left  dorsal — were  male,  as 
proved  by  the  smaller  size  of  the  parts  themselves  and  of  their  bristles,  and 
even  better  by  the  presence  of  a  sex-comb  upon  the  right  foreleg  and  of  a 
miniature  wing  of  male  size  upon  the  left  side.  As  the  head  was  entirely 
female,  the  abdomen  seemed  to  be  entirely  male,  except  that  the  armature 
seemed  slightly  different  in  the  two  sides  of  the  penis. 

Explanations. — An  egg  carrying  an  eosin  miniature  X  (whether  or  not  a 
Y  also  is  unknown)  was  fertilized  by  the  X  sperm  carrying  only  wild-tyix? 
genes.  Elimination  of  a  paternal  X  occurred.  The  segmentation  nuclei 
descended  from  this  same  pair  of  male  and  female  cells  were  distributed  in  a 
regular  but  complex  pattern. 

No.  941.     December  15,  1914.     C.  B.  Bridges.     Text-figure  46  (diagram). 

Parentage. — The  parentage  is  somewhat  uncertain,  probably  as  follows: 
The  mother  had  one  X  with  eosin,  notch,  tan,  and  vennilion,  and  the  other 
X  wild-type.     The  father  was  eosin  tan  vermiHon. 

Description. — The  gynandromorph  was  about  half-and-half,  but  rather 
complex  in  the  distribution  of  male  and  female  parts.  The  head  was  large, 
therefore  probably  female.  The  eyes  were  aUke  and  vermilion.  The  right 
wing  was  a  typical  notch  (female)  but  was  only  doubtfully  larger  than  the 
left.     The  abdomen  was  female  in  coloration  anteriorly  but  male  posteriorly. 


56 


THE    ORIGIN   OF   GYNANDROMORPHS. 


The  genitalia  were  largely  male,  but  had  female  parts  on  the  right  side.  A 
pair  of  rudimentary  ovaries  were  present.  There  were  sex-combs  on  both 
forelegs,  so  that  the  ventral  side  of  the  thorax  was  entirely  male.  The  fly  was 
tan  throughout. 

Explanations. — An  egg  containing  a  cross-over  chromosome  with  the  genes 
for  notch,  tan,  and  vermilion  was  fertilized  by  an  X  sperm  carrying  eosin, 
tan,  and  vermihon.  Elimination  of  the  maternal  X  was  followed  by  shifting 
of  the  cleavage  nuclei. 


N 


t 


w" 


t 


w^ 


t 


No.  983.     December  20, 1914.     C.B.  Bridges.     Text-figure  47  (diagram). 

Parentage. — One  of  the  X  chromosomes  of  the  mother  carried  the  genes  for 
white  and  for  bar,  and  the  other  X  the  gene  for  eosin.  The  father  was 
miniature. 

Description. — The  separation  of  the  sex-characters  is  very  complex.  The 
dorsal  parts  of  the  thorax  and  the  wings  are,  from  their  size,  female ;  the  lower 


Text-figure  45. 


TEXT-riGURE  46. 


Text-figure  47. 


part  of  the  thorax,  from  the  presence  of  sex-combs  on  both  forelegs,  is  male. 
The  abdomen  is  female  on  the  left  half  and  male  on  the  right.  The  genitalia 
are  female.  The  abdomen  contained  a  pair  of  ovaries  as  seen  through  the 
body-wall  and  in  sections.  The  fly  was  sterile.  The  head  was  entirely  male, 
with  white  eyes,  not-bar. 


THE   ORIGIN   OF   GYNANDROMORPHS.  57 

Explanations. — A  cross-over  X  carrying  the  gene  for  white  but  not  for  bar 
was  present  in  the  egg,  which  was  fertihzed  by  the  X  sperm  carrying  the 
gene  for  miniature.  Elimination  of  this  paternal  X  left  a  cell  with  the  white 
X  to  determine  the  male  parts.  In  the  early  cleavage  there  must  have  been 
extensive  shifting  of  the  nuclei  to  produce  the  observed  mosaic  of  female  and 
male  parts. 

w  V 


m 

No.  16240521114.     Selection  Experiment.     August  2,  1916.     T.  H.  Morgan. 

Plate  4,  Figure  2  (drawing). 

Parentage. — The  gynandromorph  arose  in  a  "selected"  notch  stock  in 
which  the  female  carried  notch  in  one  X  and  eosin  and  ruby  in  the  other. 
The  father  was  eosin  ruby. 

Description. — The  gynandromorph  was  "quartered,"  being  male  in  the 
anterior  left  section  and  also  in  the  posterior  right  section,  and  female  in  the 
two  other  sections.  The  left  eye  was  mainly  eosin  ruby,  but  had  a  small 
section  of  red  (female)  pushed  in  from  the  rear.  The  left  side  of  the  thorax 
was  male,  as  evidenced  by  the  sex-comb  and  the  shorter  wing.  The  right 
side  of  the  abdomen  had  male  coloration  above  and  below,  and  the  genitalia 
were  male  on  the  right  side  and  female  on  the  left.  The  abdomen  seemed  to 
have  a  pair  of  ovaries  when  examined,  but  the  sections  made  later  were  too 
poor  to  confirm  this.     The  right  eye  was  red  and  the  right  wing  notch. 

Explanations. — ^An  egg  carrying  the  gene  for  notch  was  fertilized  by  a  sperm 
carrying  the  genes  for  eosin  and  ruby.  Elimination  of  the  maternal  notch 
X  occurred  at  the  first  division,  leaving  the  eosin  ruby  paternal  X  to  determine 
the  character  of  the  male  parts.  The  products  of  the  second  division  rear- 
ranged themselves  so  that  sister  cells  took  part  in  the  development  of  opposite 
sides  of  the  body.  This  is  only  a  little  more  extreme  than  the  usual  rear- 
rangement and  shifting  of  parts  (see  patch  of  red  in  left  eye). 


10*         n  w  n 

SPECIAL  CASES. 

The  following  cases  were  brought  together  because  they  could  not 
be  explained  simply  by  the  theory  of  ehmination.  Analysis  showed 
that  in  each  of  these  cases  there  were  present  two  different  chromo- 
somes, both  derived  from  the  mother.  Non-disjunction  obviously  offered 
an  explanation  for  this  fact.  But  the  application  of  this  hypothesis 
required  the  additional  assumption  of  "somatic  reduction"  to  explain 
the  gynandromorphism.  This  means  that  at  an  early  division  the 
two  X's  derived  from  the  mother  separate  without  division.  On 
the  other  hand,  if  we  assume  for  these  cases  that  both  sex  chromosomes 
leave  a  daughter  half  at  the  mid-plate  (double  elimination)  the  assump- 
tion just  stated  is  avoided.  Until  further  explanation  is  obtained 
these  two  interpretations  may  be  given  as  alternatives. 


58 


THE    ORIGIN   OF   GYNANDROMORPHS. 


Doncaster's  observations  on  binucleated  eggs  of  Abraxas,  where 
both  nuclei  underwent  separate  reduction  and  fertihzation,  ofifer  a 
simpler  explanation.  On  the  other  hand,  it  should  be  pointed  out 
that  there  should  have  been  at  least  as  many  autosomal  mosaics  as 
sex-linked  mosaics  produced  by  fertilization  of  binucleated  eggs  of 
heterozygous  mothers;  and  this  does  not  seem  to  be  the  case. 


No.  B.  90.     June  17,  1912.     C.  B.  Bridges.     Text-figure  48  (drawing). 

Parentage. — This  gynandromorph  appeared  in  F2  from 
the  cross  of  rudimentary  female  to  white  miniature  male; 
that  is,  the  mother  (F,  female)  carried  rudimentary  in 
one  X  and  white  and  miniature  in  the  other;  and  the  father 
was  a  rudimentary  (Fi)  male. 

Description. — The  individual  seemed  to  be  male  through- 
out. Both  eyes  were  red.  Sex-combs  were  present  on 
both  forelegs.  The  right  wing  was  long,  and  though 
slightly  deformed,  was  undoubtedly  wild-type.  The  left 
wing  was  a  typical  and  perfect  miniature  rudimentary 
wing.  The  abdomen  was  entirely  male,  and  when  mated 
to  a  vermilion  female  the  fly  bred  as  a  male,  producing 
abundant  offspring.  Several  pairs  of  the  wild-type  daugh- 
ters and  vermilion  sons  of  this  mating  were  bred  and  all 
produced  red  and  vermilion  in  equal  numbers,  both  in  males 
and  females.  That  is,  the  gynandromorph  bred  as  a  wild- 
type  male  carrying  no  mutant  genes.  Two  of  the  F2  pairs 
are  given  as  samples: 


Text-figure  48. 


Wild-type  9 

Wild-type  (f 

Vermilion  9 

Vermilion  cT 

B.  98.1 
B.  98.2 

45 
26 

33 
16 

32 
30 

43 
33 

The  drawing  has  been  previously  figured  in  Zeit.  f.  ind.  Abst.  und  Verer., 
1912,  p.  324. 

Explanations. — Simple  elimination  fails  to  explain  this  case,  because  the 
characters  of  the  fly,  as  well  as  its  genetic  behavior,  show  that  it  received  two 
different  X  chromosomes  from  its  mother.  For  instance,  miniature  and 
rudimentary  were  both  present  in  the  left  (male)  wing,  which  proves  that  the 
X  contained  in  these  parts  came  from  the  mother  and  that  crossing-over  in  the 
mother  must  have  occurred.  Since  the  right  wing  was  wild-type,  its  cells 
must  have  contained  a  wild-type  X,  which  likewise  could  only  have  come  from 
the  mother.  The  Fi  and  F2  offspring  of  the  gynandromorph  showed  that  he 
had  such  a  wild-type  X  in  the  testis,  which  presumably  came  from  the  same 
kind  of  cells  as  those  of  the  right  side.  The  offspring  also  show  that  the 
gynandromorph  had  not  received  an  X  sperm  from  the  father,  which  would 
have  given  rudimentary  offspring.  Therefore  the  right  side,  at  least,  must 
have  come  from  a  Y-bearing  sperm,  as  further  proved  by  the  fact  that  the 
gynandromorph  was  fertile  as  a  male  (males  without  a  Y  being  sterile). 

On  the  view  that  the  gynandromorph  came  from  an  egg  with  two  nuclei, 
a  simple  explanation  of  the  result  may  be  given.  Before  reduction,  each 
of  the  postulated  nuclei  must  have  had  one  white  miniature  X  and  one  red 
rudimentary  X  chromosome;  after  crossing-over  and  reduction  in  each,  one 


THE   ORIGIN    OF   GYNANDROMORPHS. 


59 


nucleus  contained  a  white  miniature  rudimentary  cross-over  X,  and  the 
other  nucleus  a  wild-t>i^e  cross-over  X.  Each  nucleus  was  fertilized  by  a 
Y-type  sperm,  proof  of  which  for  the  right  side  has  been  given;  proof  for  "left 
side  is  as  follows:  The  left  wing  is  miniature  as  well  a*  rudimentary,  and  since 


Text-figure  49. 


Text-figure  50. 


Text-figure  51. 


the  X  of  the  father  did  not  carry  miniature,  this  left  side  could  not  have 
contained  a  paternal  X  and  must  therefore  have  contained  a  paternal  Y 
chromosome. 

One  of  the  cross-over  chromosomes  was  white  as  well  as  miniature  and 
rudimentary;  but  since  the  eye  on  the  side  with  miniature  was  red,  we  may 
suppose  that  all  of  the  head  came,  as  is  very  often  the  case,  from  cells  from 
one  side  only,  namely,  the  right,  which  was  here  carrying  red;  or  this  cross- 
over chromosome  may  have  come  from  double  crossing-over,  and  in  this  case 
it  would  have  carried  red. 


Lejl  side. 


Right  side. 


W 


m 


VI 


or 


On  an  alternative  view  that  both  of  these  X's  were  in  a  single  nucleus,  the 
following  assumption  seems  necessary.  An  XX  egg  was  produced  by  reduc- 
tional  primary  non-disjunction  (see  Bridges,  1916),  preceded  by  crossing-over, 
so  that  one  X  contained  white  miniature  rudimentary  and  the  other  was  the 
complementary  X  containing  only  wild-type  genes.  This  XX  egg  wa:?  then 
fertilized  by  a  Y  sperm. 

That  the  individual  was  entirely  male  with  no  female  parts  can  be  explained 
either  by  double  elimination  or  somatic  reduction  at  the  first  division  of  the 
zygote;  that  is,  one  member  of  each  pair  was  caught  by  the  elimination  plate, 


60  THE    ORIGIN   OF   GYNANDROMORPHS. 

SO  that  each  of  the  two  first  daughter  cells  had  but  one  X  and  these  different 
from  each  other. 

Zygote.  Left  side.  Right  side. 

w  m        r  w         m        r 

■  I         I  III 

1 X  ! X  Y 


No.  I  92.     August  16,  1913.     C.  B.  Bridges.     Text-figure  49  (diagram). 

Parentage. — One  of  the  X  chromosomes  of  the  mother  carried  the  genes  for 
vermiHon  and  for  fused  and  the  other  X  the  gene  for  bar.  The  father  was 
vermilion  fused. 

Description. — The  gynandromorph  was  completely  bilateral,  except  for 
the  genitalia,  which  were  female.  The  left  side  was  male,  as  evidenced  by 
the  smaller  size  throughout,  by  the  sex-comb,  and  by  male  coloration  on  the 
abdomen.  The  left  eye  was  bar  of  the  male  type.  The  right  side  was  female 
in  every  part,  and  was  chiefly  remarkable  in  that  its  large  wing  was  fused. 
The  eyes  were  both  red,  not  vermilion.  The  right  eye  was  round,  not  hetero- 
zygous bar.     A  pair  of  ovaries  was  found  in  the  sections. 

Explanations. — On  the  assumption  of  two  nuclei  in  the  egg,  one  nucleus  after 
reduction  contained  a  non-cross-over  bar  X  chromosome,  and  this  nucleus 
fertilized  by  a  Y  sperm  gave  the  bar  male  left  side,  with  bar  eye;  the  other 
nucleus  after  crossing-over  and  reduction  contained  a  cross-over  fused  X 
chromosome,  wh  ch  nucleus  fertilized  by  the  vermilion  fused  X  spenn  gave 
the  female  right  side  with  fused  wing: 

Left  side.  Right  side. 

B  fu 


On  the  alternative  view  that  both  X's  from  the  mother  were  retained  after 
reduction  in  the  same  nucleus  of  the  egg,  the  case  is  difficult,  but  may  be 
accounted  for  in  the  following  way:  Since  the  left  side  is  male  throughout 
and  shows  the  bar  eye-character  (of  male  type),  this  side  must  have  come  from 
a  non-cross-over  X  of  the  mother.  But  this  bar  X  is  not  represented  at  all 
on  the  right  side,  as  proved  by  the  round  eye,  which,  although  female,  is 
not  even  heterozygous  for  bar.  That  the  right  side  is  female  requires  that 
two  X's  be  present,  and  the  fact  that  the  wing  is  fused  requires  that  both 
carry  the  fused  gene.  A  non-cross-over  vermilion  fused  X  must  have  come 
from  the  mother  along  with  the  bar  X.  The  egg,  then,  was  an  XX  egg  pro- 
duced by  primary  non-disjunction  which  was  equational,  since  the  bar  X 
was  a  non-cross-over  and  the  fused  X  a  cross-over  chromosome  (Bridges, 
1916).  This  XX  egg  was  fertilized  by  an  X  sperm  carrying  the  genes  for 
vermilion  and  for  fused.  It  is  known  that  XXX  zygotes  are  unable  to 
hatch  as  adult  flies  (Bridges,  1916),  but  since  neither  the  time  nor  the  mechan- 
ism of  their  elimination  is  known,  it  is  possible  that  if  double  elimination  or 
somatic  reduction  followed  soon  after  fertilization  the  life  of  the  XXX 
individual  would  be  saved,  hut  at  the  price  of  becoming  a  gynandromorph. 
Two  of  the  X's,  in  this  case  the  paternal  vermilion  fused  and  the  maternal 


THE    ORIGIN   OF   GYNANDROMORPHS.  61 

fused  cross-over  X,  remained  in  one  cleavage  cell  which  gave  rise  to  the  not- 
vermilion  not-bar  fused  female  right  side.  The  other  X,  the  maternal  non- 
cross-over  bar  X,  passed  into  the  other  daughter  cell  and  gave  rise  to  the 
not-vermilion  bar  not-fused  left  side. 

-    Zygote.  Left  side.  Right  side. 

V  fu 


V                      Ju 
•                           1 

^" 

B 


B 

No.  937.     December  17,  1914.     C.  B.  Bridges.     Text-figure  50  (diagram). 

Parentage. — The  grandmother  was  a  wild-type  XXY  female  carrying  the 
genes  for  eosin  and  vermilion  in  one  X  and  in  the  other  only  wild-type  genes; 
the  grandfather  was  white  bar.  By  equational  non-disjunction  an  XXY  eosin 
daughter  was  produced  which  carried  eosin  and  vermilion  in  one  X  and  eosin 
in  the  other.  This  female  was  out-crossed  to  a  vermilion  male  and  produced 
among  the  sons  a  mosaic. 

Description. — The  mosaic,  as  in  the  case  B  90,  was  male  throughout,  but 
the  left  eye  was  eosin  (of  the  male  type)  and  the  right  eye  was  eosin  vermilion. 
The  male  was  fertile  when  bred  to  a  vermilion  female,  giving  wild-type 
daughters  and  vermilion  sons  (No.  1116).  One  of  the  wild-type  daughters 
out-crossed  to  a  forked  male  gave  eosin  and  vermilion  as  the  main  classes  of 
the  sons. 

Explanations. — On  the  hypothesis  of  a  binucleated  egg,  one  nucleus  after 
reduction  contained  an  eosin  vermilion  X  and  the  other  nucleus  an  eosin  X. 
Since  no  eye-color  corresponded  to  the  X  sperm  of  the  father,  and  since  the 
individual  was  male  throughout,  both  of  the  egg-nuclei  must  have  been 
fert  lized  by  a  Y  sperm,  which  is  further  shown  by  the  fertility  of  the  male. 

Left  side.  Right  side. 


On  the  view  that  a  single  nucleus  was  present,  the  following  situation  de- 
velops: Since  the  right  eye  showed  both  eosin  and  vermilion,  the  mosaic 
must  have  contained  the  eosin  vermilion  X  of  the  mother.  Since  the  other 
eye  showed  eosin  (not  vermilion), this  X  must  have  been  the  other  or  eosin  X 
of  the  mother.  That  is,  both  X  chromosomes  of  the  mosaic  came  from  the 
mother  by  means  of  an  XX  egg  produced  through  non-disjunction.  The  ver- 
milion X  of  the  father  was  not  present  at  all,  as  proved  by  the  fact  that  the 
left  eye  of  the  mosaic  was  eosin  (not  red)  and  male  (not  female), and  by  the 
breeding-test,  which  showed  that  the  gonads  carried  only  the  eosin  X.  The 
sperm  was  not  the  X  sperm  of  the  father,  but  the  Y  sperm,  as  further  indicated 
by  the  fertility  of  the  male. 

As  in  case  B  90,  there  must  have  been  double  elimination  or  somatic  re- 
duction, so  that  one  cleavage-cell  received  the  eosin  X  and  a  Y,  and  the  other 


62  THE    ORIGIN   OF   GYNANDROMORPHS. 

the  eosin  vermilion  X  and  a  Y.     The  gonads  developed  from  an  eosin  cell  as 
shown  by  the  Fj  and  F2  results  of  his  breeding  test. 

Zygote.  Left  bide.  Right  side. 


w*  w^ 


No.  1333.    February  19,  1915.    C.  B.  Bridges.    Text-figure  51  (diagram). 

Parentage. — The  mother  was  a  wild-type  XXY  female,  carrying  the  genes 
for  eosin  in  one  X  and  for  vermilion  and  forked  in  the  other.  The  father  was 
bar. 

Description. — The  fly  was  female  throughout,  except  for  the  left  eye  which 
was  round  (not  bar)  and  red  (not  eosin  or  vermilion).  The  eye  has  been 
examined  repeatedly  at  different  times  since  the  mosaic  was  on  hand,  and  the 
eye  is  undoubtedly  not-bar  and  is  of  the  right  size  for  a  male.  The  right 
eye  was  heterozygous  bar.  There  were  no  forked  bristles  present  around  the 
left  eye  elsewhere.  The  female  was  mated  to  a  sable  forked  male  and  pro- 
duced: No.  1555 — forked  females,  11;  forked  bar  females,  0;  bar  females,  18; 
wild-type  female,  1;  vermilion  forked  males,  18;  bar  males,  6;  vermilion  bar 
males,  3;  forked  males,  2. 

Explanations. — On  the  hypothesis  of  a  binucleated  egg,  one  nucleus  after 
reduction  contained  a  cross-over  wild-type  X  and  the  other  a  non-cross-over 
vermilion  forked  X  chromosome.  The  former  fertilized  by  a  Y  sperm  gave 
rise  to  the  wild-type  (male)  left  eye;  the  latter  fertilized  by  a  bar  X  sperm 
gave  rise  to  the  rest  of  the  fly. 

Lejt  side.  Right  side. 

V  f 


B 

The  following  alternative  possibilities  may  be  considered:  The  simplest 
possible  explanation  is  that  this  is  a  mosaic  or  somatic  mutation — that  the 
bar  gene  in  the  cell  that  gave  rise  to  the  left  eye  reverted  to  not-bar,  or  to  an 
allelomorph  which  gives  a  small  round  eye.  If,  as  is  more  probable,  this 
mosaic  is  a  gynandromorph  arising  by  chromosomal  disturbance,  the  ex- 
planation is  like  that  for  No.  I  92,  i.  e.,  the  egg  arose  by  equational  non-dis- 
junction and  contained  a  non-cross-over  vermilion  forked  X  and  a  cross-over 
wild-type  X.  This  egg  probably  did  not  contain  a  Y,  as  evidenced  by  the 
lack  of  exceptions  among  the  sons  of  the  mosaic,  and  as  is  possible  in  accordance 
with  the  assumption  of  equational  non-disjunction,  for  equational  non-dis- 
junction, even  when  occurring  in  a  female  with  a  Y,  is  probably  always  primary. 
One  eye  was  clearly  heterozygous  bar;  hence  it  is  known  that  the  XX  egg 
was  fertilized  by  an  X  sperm  carrying  the  gene  for  bar.  This  XXX  zygote 
would  ultimately  die,  unless  at  an  early  stage  the  XXX  condition  was  cor- 
rected by  reduction  or  elimination.  Double  elimination  or  somatic  reduction 
in  a  cleavage-cell  would  save  the  individual,  but  turn  it  into  a  gynandromorph. 
The  other  X  chromosome,  wild-type,  passed  into  the  sister  cell  and  gave  rise 


THE    ORIGIN   OF   GYNANDROMORPHS. 


63 


to  male  parts,  which,  because  of  the  lateness  of  the  occurrence,  or  from  shift- 
ing of  nuclei,  constituted  but  a  small  part  of  the  gynandromorph. 


Zygote. 
V 

1 

/ 

1 

X 
X 

X 

Left  side. 

X 

liiyhl  side. 

f 

1                                1 

X 

X 

B 

B 


No.  2349.     November  3.  1915.     C.  B.  Bridges.     Text-figure  52  (drawing). 

Parentage. — The  mother  was  from  a  strain  of  high  non-<lisj unction,  but  was 
known  to  be  XX  and  not  XXY.  One  X  carried  the  genes  for  vermilion  and 
forked,  the  other  X  the  gene  for  bar.  The  father  was  a  vermilion  forked 
male. 

Description. — The  gynandromorph  was  largely  male.  The  female  parts 
included  the  left  legs,  which  were  without  a  sex-comb  and  had  forked  bristles. 
The  female  parts  throughout  had  forked  bristles  and  could  therefore  be 
readily  traced.  All  three  left  legs  were  forked  and  female  to  the  mid-ventral 
line.     A  very  narrow  strip  of  female  tissue  ran  diagonally  forward  from  above 


Text-figuke  52. 


Text-figure  53. 


the  middle  left  leg  to  the  shoulder,  being  chiefly  marked  by  one  large  forked 
bristle  and  several  smaller  ones.  Most  of  the  left  side  of  the  head  bore  forked 
bristles,  including  the  left  antenna,  the  dorsal  region  to  the  left  of  the  line 
in  the  diagram,  a  small  zone  of  tissue  around  the  eye  to  the  rear,  and  the  region 
below  the  eye  including  the  oral  bristles.  The  left  eye  was  red  (not  vermilion) 
and  round  (not  bar  or  heterozygous  bar — the  small  nick  seen  in  the  drawing 
of  the  eye  seems  to  be  an  artifact).     The  abdomen  was  male  type,  the  genitalia 


64  THE    ORIGIN   OF   GYNANDROMORPHS. 

were  half  and  half,  the  left  half  bearing  a  female  type  anal  prominence  with 
forked  bristles.  Sections  showed  that  ovaries  were  present  with  well-devel- 
oped eggs,  which  account  for  the  large  size  anteriorly  of  male-type  abdomen. 
The  male  parts,  as  distinguished  by  the  normal  bristles,  included  the  whole 
dorsal  surface  of  the  thorax,  the  two  wings,  which  were  of  equal  size  (male), 
the  abdomen  (except  for  half  the  genitalia),  all  the  right  legs,  and  somewhat 
more  than  the  right  side  of  the  head.  The  right  foreleg  bore  a  sex-comb. 
The  right  eye  was  bar  (male  type),  not  vermilion  in  color. 

Explanations. — On  the  theory  that  two  nuclei  were  present  in  the  egg,  one 
nucleus  contained  after  reduction  a  cross-over  forked  X,  the  other  nucleus  a 
bar  X  chromosome.  The  former  fertilized  by  a  vermilion  forked  X  sperm 
gave  rise  to  the  female  parts  on  the  left  side,  the  latter  fertilized  by  a  Y 
sperm  gave  rise  to  the  left  male  side,  with  the  bar  eye,  etc. 

Left  side.  Right  side. 

f  B 


V  f 

On  the  assumption  of  a  single  nucleus  in  the  egg  a  possible  explanation  is  as 
follows:  The  male  parts  show  the  character  bar,  and  since  bar  was  present 
only  in  the  mother,  they  are  known  to  have  been  derived  from  the  maternal 
bar  X,  which  was  a  non-cross-over  X,  since  the  eye  did  not  show  the  character 
vermilion.  The  female  parts  were  forked,  but  since  the  eye  was  not  vermilion, 
one  of  the  forked  X's  must  have  been  a  cross-over  between  vermilion  and 
forked.  Crossing-over  takes  place  only  in  the  female  and  not  in  the  male, 
wherefore  this  X  also  is  known  to  have  come  from  the  mother.  One  cross- 
over and  one  non-cross-over  X  is  the  general  rule  for  eggs  produced  by  primary 
equational  non-disjunction.  The  other  forked  X  must  have  come  from  the 
father  and  therefore  carried  the  gene  for  vermilion;  but  vermilion  is  recessive 
and  its  effect  is  hidden  by  the  normal  allelomorph  in  the  cross-over  X  from 
the  mother.  The  gynandromorph,  as  in  cases  192  and  1333,  started  as  a 
XXX  zygote  which  was  saved  from  death  and  at  the  same  time  converted 
into  a  mosaic  by  double  elimination  or  somatic  reduction  at  the  first  cleavage 
division. 

Zygote.  Left  side.  Right  side. 

B  f  B 


f__  V  f 

/ 
No.  4241.     May  15,  1916.     C.  B.  Bridges.     Text-figure  53  (diagram). 

Parentage. — One  of  the  X  chromosomes  of  the  mother  carried  the  genes  for 
lethal  7  and  ruby  eye-color,  the  other  X  the  genes  for  yellow,  eosin,  and 
forked.  The  X  chromosome  of  the  father  carried  the  genes  for  yellow,  eosin, 
and  forked. 

Description. — The  right  side  was  male  throughout,  except  that  in  the  head 
the  female  part  (bordered  by  the  dashed  line  in  the  diagram)  extended  nearly 
to  but  did  not  include  the  right  eye.     The  right  eye  was  smaller  and  ruby. 


THE    ORIGIN    OF   GYNANDROMORPHS.  65 

The  two  anterior  bristles  above  the  right  eye  and  all  the  bristles  below  it  were 
forked,  agreeing  with  the  forked  bristles  present  throughout  the  rest  of  the 
right  side  on  legs,  thorax,  and  abdomen.  A  sex-comb  was  present  on  the 
right  fore-leg  and  all  male  parts  were  smaller.  The  right  side  was  female 
throughout,  with  normal  bristles  and  a  red  eye.  The  genitalia  were  half- 
and-half.  In  the  sections  of  the  abdomen  an  ovary  could  be  identified  on  one 
side,  less  certainly  on  the  other.  The  body-color  of  both  male  and  female 
parts  was  wild-type  throughout,  with  no  yellow. 

Explanations. — On  the  theory  of  the  binucleated  egg,  one  nucleus  contained 
an  X  with  the  genes  for  lethal  and  ruby,  the  other  nucleus  a  cross-over  X 
with  the  genes  for  lethal,  ruby,  and  forked.  The  former  fertilized  by  X  sperm 
with  yellow  eosin  forked,  produced  a  female  left  side  with  only  wild-tyj^e 
characters;  the  latter,  fertilized  by  a  Y  sperm,  gave  the  ruby  forked  male 
side. 

Left  side.  Right  side, 

y     W'  f  It       r^  f 


An  alternative  view  based  on  a  single  nucleus  is  as  follows :  Simple  elimina- 
tion fails  to  explain  the  case,  since  the  male  parts  that  are  forked  are  not- 
yellow  and  not-eosin,  as  might  be  expected,  but  instead  were  ruby.  Since 
ruby  was  present  only  in  the  mother,  the  male  parts  must  have  come  from  a 
lethal  7  ruby  forked  cross-over  chromosome  produced  by  the  mother.  That 
the  other  X  chromosome  of  the  zygote  was  not  the  yellow  eosin  forked  X  of 
the  father  is  proved  by  the  not-forked  character  of  the  female  parts.  It 
seems  certain  that  both  X  chromosomes  of  the  zygote  came  from  the  mother, 
that  is,  that  the  egg  was  a  non-disjunctional  XX  egg.  This  must  have  been 
by  primary  non-disjunction,  since  the  pedigree  is  fully  known  and  no  other 
exceptions  were  produced.  Another  fact  points  to  the  same  conclusion, 
namely,  that  these  X's  were  both  cross-overs,  and,  as  Bridges  has  shown,  both 
X's  of  secondary  exceptions  are  always  non-cross-overs.     What  occurred,  then, 

y        rV                        f 
was  crossing-over  in  the  — '—, — '• i '■ female  between  the 

loci  ruby  and  forked.  Owing,  perhaps,  to  some  entanglement  in  the  process  of 
crossing-over,  the  chromosomes  were  unable  to  separate  in  time  for  the  reduction 
division  and  both  were  retained  in  the  egg.  This  egg,  containing  a  yellow  eosin 
X  and  a  lethal  7  ruby  forked  X,  was  fertilized  by  a  Y  sperm.  At  the  first 
segmentation  divisions  one  of  these  maternal  yellow  eosin  chromosomes  was 
eliminated,  giving  a  gj'nandromorph  whose  male  parts  were  lethal  7,  ruby, 
and  forked. 

Left  side.  Right  side. 

h  Th  f  h  Th  f 


y     w  J 


A  very  interesting  point  in  connection  with  gj'nandromorph  4241  is  the 
fact  that  a  male  part,  which  must  be  assumed  to  have  the  lethal  7  gene,  was 
able  to  live  when  associated  with  the  not-lethal  partner  in  the  gj'nandromorph. 
This  is,  however,  understandable  when  the  nature  of  the  action  of  the  lethal  7 


66 


THE   ORIGIN    OF   GYNANDROMORPHS. 


gene  is  considered.  Normally,  the  males  which  possess  the  lethal  7  gene 
not  only  begin  development,  but  continue  often  to  the  full-grown  larva  stage. 
The  immediate  cause  of  their  death  at  this  late  stage  is  the  development  of 
one  or  more  black  granules  which  cause  death  either  because  they  are  them- 
selves toxic  or  because  their  substance  is  derived  from  an  excessive  malforma- 
tion of  organs  essential  to  the  further  development  of  the  fly.  On  the  first 
view,  either  the  half  amount  of  toxic  body  was  insufficient  to  prevent  the 
gynandromorph  from  continuing  its  development,  or  the  corresponding  normal 
parts  of  the  female  side  counteracted  this  toxic  effect;  on  the  second  view,  the 
lack  of  the  essential  organ  on  the  male  side  was  supplied  by  the  normal  organ 
of  the  female  side. 

No.  3674.     August  9,  1917.     A.  H.  Sturtevant.     Text-figure  54  (diagram). 

Parentage. — One  of  the  X  chromosomes  of  the  mother  carried  the  genes  for 
cut,  vermihon,  and  for  forked;  the  other  X  the  gene  for  rugose.  The  father 
was  rugose  forked. 

Description. — The  male  parts  of  the  gynandro- 
morph constituted  the  left  side  of  the  thorax  and 
abdomen,  as  indicated  by  the  smaller  size,  the  sex- 
comb,  the  smaller  wing,  and  the  male  coloration  of 
that  side  of  the  abdomen.  Testes  were  found  in  the 
abdomen.  The  left  wing  showed  the  character  cut. 
The  bristles  of  all  male  parts  were  wild-type.  The 
bristles  of  the  female  parts  were  forked,  and  this 
character  forms  the  most  useful  index  of  the  divi- 
sion-line. The  entire  head,  including  the  bristles 
above  and  below  and  around  the  left  as  well  as  the 
right  eye,  was  'forked.  The  first  and  second  leg  on 
the  right  side  were  forked,  the  third  was  not  forked 
and  presumably  therefore  male.  The  bristles  on 
the  right  wing  and  on  the  right  side  of  the  abdo- 
men were  forked.  There  was  no  sex-comb  on  the 
right  side.  The  right  wing  was  of  female  size  and 
not  cut.  Both  eyes  were  red  (not  vermilion)  and 
also  not  rugose. 

Explanations. — On  the  theory  of  two  nuclei,  one 
nucleus  contained  a  cross-over  X  with  the  gene  for 
cut  and  rugose,  the  other  an  X  with  the  genes  for  cut 
vermilion  forked.  The  former  nucleus  was  fertilized 
by  a  Y  sperm  to  produce  the  left  side,  the  latter 
nucleus  by  an  X  sperm  with  rugose  and  forked  to  produce  the  female  right 

side. 

Left  side.  Right  side. 


Text-figure  54. 


d 


rg 


ct 


f 


rg 


f 


An  alternative  explanation  on  the  assumption  of  a  single  nucleus  follows: 
The  mechanism  in  this  case  must  be  essentially  the  same  as  in  cases  I  92, 
1333,  and  2349  already  given.  The  female  parts  were  entirely  forked,  there- 
fore two  forked  chromosomes  were  present.  One  of  these  could  have  come 
from  the  father,  whose  X  was  rugose  forked ;  the  other  X  could  have  come  from 


THE    ORIGIN   OF   GYNANDROMORPHS. 


67 


the  mother,  and  could  have  been  the  non-cross-over  cut  vermilion  forked  X. 
Neither  cut  nor  vermilion  would  show  in  the  female  parts,  since  they  would 
be  recessive  to  their  wild-t^-pe  allelomorphs  in  the  rugose  forked  X;  and  like- 
wise rugose  would  not  show,  for  it  would  be  recessive  to  its  wild-type  allelo- 
morph in  the  cut  vermilion  forked  X.  Both  of  these  X's  could  not  have  come 
from  the  father,  for  in  that  case  both  eyes  would  have  been  rugose.  One  of 
the  forked  X's  therefore  came  from  the  mother.  The  left  wing  was  cut,  and 
since  cut  was  present  only  in  the  mother,  this  X  also  must  have  come  from 
the  mother.  Since  the  cut  side  did  not  show  forked,  this  cut  X  must  have 
been  a  cross-over  anywhere  between  cut  and  forked.  Thus  we  see  that  the 
egg  contained  two  X's  which  were  different,  one  being  the  non-cross-over  cut 
vermilion  forked  X  and  the  other  the  cross-over  cut  X,  which  is  the  normal 
condition  of  XX  eggs  produced  by  primary  equational  non-disjunction. 
This  XX  egg  was  fertilized  by  the  rugose  forked  X  sperm  of  the  father,  giving 
an  XXX  zygote.  At  the  first  segmentation  division,  double  elimination  or 
somatic  reduction  occurred,  thereby  enabling  the  fly  to  survive,  but  only 
at  the  price  of  becoming  a  gynandromorph.  The  paternal  (rugose  forked) 
and  one  of  the  maternal  X's  (cut  vermilion  forked)  entered  one  cell,  from 
which  developed  the  female  right  side,  which  showed  only  one  mutant  char- 
acter, namely,  forked.  The  cross-over  maternal  X  (cut  vermilion?  rugose? 
not-forked)  entered  the  other  cell  and  gave  rise  to  the  male  left  side,  showing 
the  mutant  character  cut  only. 

It  should  be  noticed  that  in  all  four  of  these  cases  it  has  been  the  paternal  X 
and  one  of  the  maternal  X's  that  have  come  together  into  the  female  part,  and 
that  the  male  part  was  in  each  case  maternal.  This  suggests  that  the  essential 
feature  of  the  reduction  is  the  active  separation  of  the  two  X's  which  ab- 
normally came  from  the  same  individual  and  the  passive  inclusion  of  the 
paternal  X  in  the  same  cell  with  either  separated  maternal  X. 


Zygote. 


Left  side. 


Right  side. 


d 


f 


ct 


f 


ct 


rg 


ct 


rg 


rg  jf 


rg     f 


No.  7730.    October  24,  1917.    C.  B.  Bridges.     Text-figure  55  (drawing). 

Parentage. — The  mother  was  a  wild- 
type  regular  XX  female  (from  a  strain 
of  high  non-disjunction)  carrying  the 
genes  for  eosin  and  forked  in  one  X 
and  only  wild-type  genes  in  the  other. 
The  father  was  bar.  No  exceptions 
were  produced  other  than  the  fol- 
lowing gynandromorph. 

Description. — The  gynandromorph 
was  almost  entirely  male.  All  parts, 
except  the  head,  were  male  and  had 
forked  bristles.  The  head  was  mainly 
female,  having  straight  bristles  and  a 
red  (not-bar)  eye  on  the  right  side,  and  on  the  left  side  a  division-line  which 
ran  forward  through  the  eye.     Above  this  line,  which  was  perfectly  clean  and 


Text-figure  55. 


68 


THE    ORIGIN   OF   GYNANDROMORPHS. 


sharp,  the  eye  was  red  and  the  bristles  wild-type;  below  the  line  the  eye- 
color  was  eosin  (male  type)  and  the  bristles  were  clearly  forked.  It  is  pos- 
sible that  the  not-eosin,  not-forked  part,  described  above  as  female,  was 
really  male,  in  which  case  the  fly  would  be  a  male  mosaic.  The  fly,  bred 
as  a  male  to  an  eosin-crimson  female,  produced  143  wild-tj^e  daughters  and 
151  eosin  crimson  sons.     Two  pairs  of  these  were  inbred  and  produced: 


No. 

Eosin  9 

Eosin 
crimson  9 

Eosin 
crimson  c?" 

Eosin 
forked  d^ 

Eosin 

Eosin 

crimson 

forked  (^ 

8056 
8057 

68 
75 

83 
84 

41 
45 

44 
46 

26 
24 

32 
25 

Explanations. — On  the  assumption  that  two  nuclei  were  in  the  egg  and  that 
the  fly  was  entirely  male,  one  nucleus  contained  an  eosin  forked  X  and  the 
other  nucleus  a  wild-type  X;  each  nucleus  having  been  fertilized  by  a  Y 
sperm,  the  former  gave  rise  to  the  eosin  forked  male  parts  and  the  latter  to 
wild-type  male  parts.  In  case  the  red  parts  were  female  the  corresponding 
nuclei  must  have  come  from  an  XX  egg  produced  by  primary  non-disjunction, 
and  likewise  fertilized  by  a  Y  sperm. 


Left  side. 


If  male. 


Right  side. 


W^ 


1/  female. 


On  the  view  that  only  one  nucleus  was  present  in  the  egg,  the  possible 
explanation  is  as  follows:  On  the  assumption  that  the  wild-type  parts  were 
female,  both  of  the  X's  present  must  have  come  from  the  mother,  since  the 
eye  was  not-bar,  as  would  have  been  the  case  if  the  X  of  the  father  were  present. 
Moreover,  that  the  sperm  was  the  Y  sperm  is  known  from  the  fact  that  the 
mother  had  no  Y  to  contribute  and  yet  the  fly  was  fertile.  The  egg  was  there- 
fore XX,  one  X  being  eosin  forked  and  the  other  wild-type,  and  was  pro- 
duced by  direct  primary  non-disjunction.  Elimination  of  the  wild-type  X 
occurred  and  the  male  cell  gave  rise  to  most  of  the  body,  including  the  gonads. 


Left  side. 


Right  side. 


W^ 


f 


W^ 


f 


On  the  assumption  that  the  wild-type  parts  were  male,  the  zygote  must 
have  had  the  same  origin  as  above,  but  double  elimination  (or  somatic  re- 
duction) occurred,  so  that  one  cell  received  a  single  eosin  forked  X  and  the 
other  a  single  wild-type  X. 


Left  side. 


Right  side. 


Vf 


f 


■X 
•Y 


■X 
-Y 


THE    ORIGIN    OF   GYNANDROMORPHS.  69 

No.Gia,62,c.    April  1914.     E.M.Wallace.    PlateS,  figure  4  (colored  drawing). 

Parentage. — The  mother  was  a  white-eosin  compound  female,  carrying  the 
genes  for  yellow  and  white  in  one  X  and  eosin  in  the  other.  The  father  was 
an  ebony  male,  used  to  show  the  lack  of  elimination  of  the  third  chromosome. 

Description. — The  mosaic  was  entirely  female.  The  right  side  of  the  thorax, 
the  right  wing,  and  the  right  legs  were  yellow  in  color,  while  the  rest  of  the 
female,  including  all  of  the  head  and  abdomen,  was  gray.  Both  wings  were 
of  the  same  size  and  there  was  no  size  inequality  in  bristles  or  other  parts. 
There  was  no  sex-comb  on  the  yellow  right  foreleg. 

Explanations. — On  the  view  that  this  gynandromorph  arose  from  a  bi- 
nuclealed  egg,  it  must  be  assumed  that  one  of  these  nuclei  must  have  contained 
two  yellow  white  bearing  X's  that  arose  through  equational  non-disjunction; 
the  other  nucleus  contained  (as  the  offspring  showed)  a  yellow  white  chromo- 
some. The  former  nucleus  fertilized  by  a  Y  sperm  gave  the  yellow  parts 
of  the  fly  (not  including  right  side  of  head,  which  is  gray  red) ;  the  latter  nucleus 
fertilized  by  wild-type  X  sperm  (from  the  ebony  male)  gave  the  left  side  of 
the  fly,  including  all  of  head  and  abdomen. 

Left  side.  Right  side. 

y    w  y    w 

I  I _^ _^ I I  „ 

X  X 

y    w 

I  I 

y        X 


If  the  mosaic  had  arisen  from  a  yellow  white  egg  fertilized  by  the  X  sperm 
of  the  ebony  male  (whose  X  chromosome  carried  only  wild-type  genes)  it 
would  have  been  easy  to  explain  the  case  as  simple  elimination  were  it  not 
that  the  yellow  parts  were  unmistakably /emaZe,  which  is  impossible  without 
the  additional  hypothesis  of  a  succeeding  somatic  non-disjunction.  It  was 
next  supposed  that  the  mechanism  of  the  production  of  the  mosaic  had  been 
double  somatic  non-disjunction,  that  the  two  daughter  wild-type  X's  had  gone 
into  the  same  cell,  giving  rise  to  the  wild-type  left-side  female  parts,  and  that 
the  two  daughter  yellow  white  X's  had  both  been  included  in  the  other  cell, 
which  gave  rise  to  the  yellow  female  parts  on  the  right  side.  On  this  hypothe- 
sis the  offspring  (disregarding  ebony)  should  correspond  to  those  of  a  pure 
yellow  white  female  or  of  a  pure  wild  female.  In  fact,  however,  the  offspring 
correspond  to  those  of  the  original  zygote  when  the  mosaic  was  mated  to  a 
yellow  white  brother:  yellow  white  females,  106;  yellow  white  males,  103; 
wild-type  females,  117;  wild-type  males,  107;  yellow  males,  2;  white  male,  1. 

A  possible  escape  from  this  dilemma  is  to  suppose  that  the  non-disjunction 
took  place  after  the  firet  division  and  that  the  normal  cell  was  the  one  which 
gave  rise  to  the  germ-cells.  This  mosaic  would  then  be  triregional — the  ab- 
domen and  gonads  heterozygous  for  yellow  and  white  and  representing  the 
original  zygote,  the  right  side  of  the  thorax  pure  yellow  white,  the  left  side  of 
the  thorax  and  the  head  pure  wild-type. 

Another  type  of  explanation  is  that  in  the  normal  XX  zygote  somatic  muta- 
tion to  yellow  occurred  in  the  wild-type  chromosome,  so  that  the  yellow  part 
contains  a  mutant  yellow  X  and  the  maternal  yellow  white  X.  Or  somatic 
deficiency  for  the  yellow  locus  occurred  in  the  wild-t}i)e  X,  so  that  the  yellow 
parts  are  haploid  for  yellow,  and  like  the  normally  haploid  male  show  yellow, 
while  these  parts  are  female  because  the  sex  gene  is  situated  in  some  other 
part  of  the  X  than  the  yellow-deficient  region. 


70 


THE    ORIGIN    OF   GYNANDROMORPHS. 


GYNANDROMORPHS  WITH  INCOMPLETE  DATA. 

A  fly  was  figured  by  Morgan  (Zeit.  f.  i.  Abst.  u.  Ver.  vii  1912,  fig.  3)  with 
one  long  wing  and  one  miniature  wing  (text-fig.  56).  Its  history  has  been 
lost,  but  it  is  recorded  in  a  paper  giving  crosses  that  involve  miniature  wings. 
The  fly  was  probably  a  gynandromorph. 

No.  28.     February  11,  1918.     T.  H.  Morgan.     Text-figure  57  (drawing). 

Parentage. — Uncertain ;  probably  the  gynandromorph  appeared  in  a  stock  of 
"serrate"  extracted  from  a  cross  of  dichsete  (carrying  serrate)  to  short  notch. 


Text-figuee  56. 


Text-figure  57. 


Description. — The  gynandromorph  was  largely  female,  the  entire  head 
and  the  right  side  of  the  thorax  with  the  right  wing  and  legs  being  male.  The 
sex-combs  seemed  to  be  only  half  as  large  as  that  of  a  normal  male. 

No.  M.     February  1912.     E.  M.  Wallace.     Text-figure  58  (diagram). 

Parentage. — The  ancestry  is  unknown. 

Description. — The  gynandromorph  was  largely  female;  the  male  parts 
being  the  right  dorsal  half  of  the  thorax  with  its  wing,  which  were  yellow  in 
color  and  of  smaller  size. 

No.  H.     July  1913.     Text-figure  59  (diagram). 

Parentage. — Ancestry  unknown. 

Description. — The  fly  was  yellow  and  female  to  all  appearances,  except  tip 
of  abdomen,  which  was  male.  A  penis  was  present.  Sections  showed  one 
abnormal  testis  and  one  broken  one. 


THE   ORIGIN    OF   GYNANDROMORPHS. 


71 


No.  G.     May  1914.     T.  H.  Morgan.     Text-figure  CO  (diagram). 

The  ancestry  is  unknown.  The  gynandromorph  was  mainly  female.  The 
fly  was  gray  with  red  eyes.  There  were  no  sex-combs  and  the  wings  were 
equal  in  length.  The  tip  of  the  abdomen  had  male  banding.  A  pair  of  ovaries 
were  seen  through  the  body-wall  and  eggs  were  found  in  section. 

No.  N.     September  1916.     T.  H.  Morgan.     Text-figure  61  (diagram). 

Parentage. — The  ancestry  is  uncertain;  probably  the  gynandromorph  came 
from  the  notch  stock.  If  so,  the  mother  carried  notch  in  one  X  and  eosin 
in  the  other,  and  the  father  was  eosin. 

Description. — The  gynandromorph  was  largely  male.  The  entire  abdomen, 
the  right  half  of  thorax,   with  wing  and  legs,  were  male.     The  division 


Text-figure  58. 


Text-figure  59. 


Text-figure  60. 


between  male  and  female  in  the  head  ran  through  the  right  eye,  which  was 
light  eosin  (male)  below  and  dark  eosin  (female)  on  the  dorsal  half. 

No.  O.     January  1912.     Text-figure  62. 

.  The  ancestry  not  recorded.  It  had  one  red  eye  (right)  and  one  white  eye 
with  a  red  fleck  in  it  (left).  On  the  left  side  there  was  a  sex-comb.  The 
wings  were  equal  in  length  and  apparently  female.  The  abdomen  and 
genitalia  were  entirely  female.     Poorly  developed  eggs  were  seen  in  section. 

No.  P.     December  1913.     Text-figure  63. 

The  ancestry  of  this  gynandromorph  is  not  recorded.  It  has  a  sex-comb 
and  short  wing  on  the  right  side.  The  abdomen  was  mostly  female,  but 
showed  some  male  parts  in  the  genitalia. 


72 


THE    ORIGIN   OF   GYNANDROMORPHS. 


No.  X.     July  15,  1916.     Text-figure  64. 

Parentage. — Ancestry  unknown. 

Description.— The  head  was  small  and  apparently  therefore  male  The 
eyes  were  eosin  ruby .  Sex-combs  were  present  on  both  sides.  The  abdomen 
was  female.     This  is  apparently  an  antero-posterior  mosaic 


Text-figure  61. 


Text-figure  62. 


Text-figure  63. 


No.  110.     December  12,  1915.     A.  Weinstein.     No  diagram. 

The  mother  had  the  genes  for  eosin,  ruby,  and  forked  in  one  X  chromosome, 
and  the  genes  for  fused  in  the  other.  The  father  was  bar.  The  eyes  of  the 
gynandromorph  were  bar  (homozygous  or  heterozygous?);  the  wings  were 
abnormal;  the  abdomen  was  female,  with  female  genitaha  somewhat  abnormal. 

DROSOPHILA  GYNANDROMORPHS  PREVIOUSLY  PUBLISHED. 

There  are  several  references  to  cases  where  white  spots  were  found  in  the 
eyes  of  Drosophila,  sometimes  in  cases  where  the  gene  for  white  eyes  might 
have  been  present  (Amer.  Naturahst,  xlvxii,  Aug.  1913,  p.  509;  Morgan, 
Science,  xxxiii,  Apr.  1911,  p.  534). 

No.  I.     J.  S.  Dexter,  1912.     Biol.  Bull.  August  1912. 

Parentage. — The  mother  carried  the  gene  for  yellow  and  white  in  one  X 
and  only  wild-type  genes  in  the  other. 

Description. — Although  the  individual  is  described  as  a  female,  it  is  more 
likely  that  the  yellow  white  right  side  was  male  and  the  wild-type  left  side 
female.  This  female  was  found  to  be  sterile,  which  agrees  better  with  the 
assumption  that  the  right  side  was  male,  since  mosaics  which  are  entirely  or 
even  more  than  half  female  usually  are  fertile. 

Explanations. — A  yellow  white  X  egg  was  fertilized  by  a  wild-type  X  sperm. 
Elimination  of  the  paternal  X  occurred. 


THE    ORIGIN   OF   GYNANDROMORPHS.  73 

In  the  early  stages  of  non-disjunction,  C.  B.  Bridges  fJourn.  Exp.  Zool, 
Nov.  1913)  found  several  gynandromorphs,  two  of  which  (N2  and  (N3)  have 
been  figured  in  Heredity  and  Sex  (p.  1G3)  and  refigured  here.  Breeding-tests 
were  tried  on  all  these  and  it  was  shown  that  some  were  fertile,  and  further 
that  the  gynandromorphs  were  not  due  to  an  inherited  condition.  It  was 
pointed  out  (p.  600)  that  such  mosaic  forms  can  be  explained  as  due  to 
somatic  non-disjunction  and  also  even  to  XXX  zygotes. 

Again,  in  the  experiments  on  "Dilution  Effects  on  Certain  Eye  Colors" 
(Morgan  and  Bridges,  J.  E.  Z.,  Nov.  1913),  about  a  dozen  gynandromorphs 
were  recorded,  most  of  which  were  sterile,  but  those  which  bred  (as  females) 
behaved  genetically  as  did  their  regular  sisters;  that  is,  they  showed  no  trace 
in  their  gonads  of  the  effect  of  the  bodily  division.  This  was  especially  strik- 
ing in  one  case  where  the  head  was  entirely  white,  yet  in  which  the  offspring 
showed  eosin  (pp.  44,  51). 

No.  I.     F.  N.  Duncan.     (See  Am.  Nat.,  vol.  49,  p.  455,  1915.) 

Parentage. — The  father  had  white  eyes,  the  mother  was  wild-type. 

Description. — The  fly  had  on  one  side  a  red  eye,  long  wing,  no  sex-comb, 
and  female  abdomen.  On  the  other  side  white  eye,  short  wing,  sex-comb, 
and  male  abdomen.  Courted  by  males  but  would  not  court.  Two  testes 
with  ripe  sperm. 

Explanations. — Elimination  of  a  maternal  X  chromosome  explains  the 
results. 

No.  II.     F.  N.  Duncan.    Plate  3,  figure  5  (colored  drawing). 

Parentage. — The  male  grandparent  was  cherry  club  vermilion,  the  female 
wild-type.  The  mother  was  heterozygous  for  the  above  genes.  The  father 
was  wild-type. 

Description. — The  fly  had  a  cherry  left  eye  and  red  right  eye.     Sex-comb 
on   left   foreleg   only.     Right   wing  shorter  than   left.     Abdomen   largely 
female,  more  female  left,   more  male  right.     Contained  two  testes  with 
immature  sperm. 

Explanations. — An  egg  containing  a  cross-over  cherry  X  was  fertilized  by 
an  X  sperm.  Elimination  of  a  paternal  chromosome  followed  by  an  irregular 
distribution  of  the  nuclei  with  one  sex  chromosome  explains  the  results. 

No.  III.     F.  N.  Duncan. 

Parentage. — Same  origin  as  No.  II. 

Description. — The  fly  had  red  eyes  and  sex-combs,  left  wing  longer,  abdomen 
male.  Genitalia  half  male,  half  female.  Was  courted  but  would  not  mate. 
Two  ovaries  with  ripe  eggs. 

Explanations. — EHmination  of  either  a  maternal  or  a  paternal  X  chromosome 
will  explain  the  result. 

No.  IV.     F.  N.  Duncan. 

Parentage. — Same  origin  as  No.  II. 

Description. — Both  eyes  red,  no  sex-combs,  wings  same  length.  Abdomen 
and  genitalia  male  on  one  side,  female  on  other.  Was  courted.  Two  testes 
with  mature  sperm. 

Explanations. — It  is  not  possible  to  determine  which  X  chromosome  was 
eliminated. 

No.  I.     1915.     Hyde  and  Powell.     Genetics,  I,  1916,  p.  580  (colored  diagram). 

Parentage. — The  mother  was  pure  for  blood,  an  allelomorph  of  white. 
The  father  was  eosin,  another  allelomorph  of  white. 


74  THE    ORIGIN   OF   GYNANDROMORPHS. 

Description. — The  mosaic  was  female  except  for  the  head,  which  was 
entirely  male.  The  left  eye  was  eosin  (male  type)  and  the  right  blood  (i.  e., 
it  was  not  eosin-blood  compound). 

Explanations. — A  blood  X  egg  was  fertilized  by  an  eosin  X  sperm.  If  at 
some  cell  division  in  the  futm^e  head  region  of  the  very  early  embryo  somatic 
reduction  occurred,  that  is,  if  the  eosin  X  went  into  one  cell  and  the  blood 
into  the  other,  neither  dividing,  both  cells  would  produce  male  parts  with 
the  eosin  and  blood  type  eyes.  The  result  may,  however,  be  explained  in 
another  way,  viz,  both  chromosomes  divided,  but  in  an  early  cell  division 
double  elimination  occurred.  One  daughter  chromosome  from  each  X  was 
caught  by  the  elimination  plate,  and  the  remaining  X's  were  left,  one  in  each  cell. 

No.  II.     1916.     Hyde  and  Powell. 

Parentage. — The  mother  had  white  eyes  and  wild-type  wings;  the  father 
had  red  eyes  and  truncate  wings  (second  chromosome). 

Description. — The  gynandromorph  had  a  white  eye  and  a  truncate  wing 
on  the  left  side  and  a  red  eye  and  wild-type  wing  on  the  right  side.  The  fly 
was  female  in  other  parts  and  when  mated  to  a  white-eyed  brother  produced : 
red  females,  75;  white  females,  70;  red  males,  65;  white  males,  65. 

Explanations. — An  egg  containing  a  white-bearing  X  was  fertilized  by  a 
red  X  sperm.  Elimination  of  a  maternal  X  left  the  male  parts  with  the 
white  X.  The  appearance  and  disappearance  of  truncate  are  so  erratic  that 
in  this  case  no  safe  conclusion  can  be  drawn  from  the  appearance  in  only  the 
male  side.  One  might  suppose  that  the  male  and  female  sides,  differing  in 
their  X  chromosomes,  also  differ  in  a  sex-linked  modifier  for  truncate. 

GYNANDROMORPHS  AND  MOSAICS  IN  BEES.^ 

The  domesticated  bees  have  furnished  many  cases  of  gynandro- 
morphs,  both  in  hives  supposedly  pure  and  in  hybrid  communities. 
An  excellent  review  of  the  recorded  cases  is  given  in  Miss  Mehling's 
paper  of  1915.  The  earliest  description  is  said  to  be  that  of  Lau- 
bender  in  1801.  Lefebure  in  1835,  Donhoff  in  1861,  Smith  in  1862, 
and  Menzel  in  1862  described  gynandromorph  bees.  Widespread 
interest  in  the  subject  was  aroused  by  the  discovery  of  many  gynandro- 
morphs  in  the  stock  of  an  apiarist,  Herr  Eugster,  in  Constance. 
Menzel  first  reported  on  this  occurrence.  It  was,  however,  von  Sie- 
bold's  account  of  the  Eugster  gynandromorphs  (1868)  that  brought 
the  subject  to  the  general  attention  of  zoologists.  He  gave  not  only 
a  description  of  many  of  these  bees,  but  dissected  them  also,  and  de- 
termined the  correspondence  or  lack  of  correspondence  between  the 
internal  sexual  organs  and  the  external  sex  characters.  In  this  hive 
there  was  a  queen  of  the  yellow  Italian  race  of  bees  (Apis  ligustica) 
fertilized  by  a  drone  of  the  darker  German  race  (Apis  mellifico).  Her 
sons  were  Italian,  which  is  the  expectation  for  this  combination.  After 
the  death  of  the  queen,  another  queen  of  ''dark  color"  was  present 
in  the  stock.     She  also  produced  some  gynandromorphs. 

^78  species  of  Hymenoptera  in  which  gynandromorphs  have  been  described  are  listed  by 
Enderlein,  including  Tenthredinidse,  Braconidae,  Proctotrupidae,  Ichneumonidae,  Formicidse,  Mutil- 
lidae,  Crabonidse,  Scoliidae,  Pompilidse,  Vespidje,  and  Aphid®  (11  families  in  all). 


THE    ORIGIN   OF   GYNANDROMORPHS.  75 

Several  other  descriptions  of  gynandromorphs  in  bees  have  been 
published  (see  Mehling,  p.  174,  and  Dalla  Torre  and  Friese,  189S). 

There  are  certain  facts  in  connection  with  sex  determination  in  the 
bee  that  are  almost  unique  and  give  an  unusual  interest  to  the  situa- 
tion. The  queen  has  the  double  set  of  chromosomes  which  is 
reduced  to  the  single  or  haploid  number  in  the  ripe  egg,  aft^r  two 
polar  bodies  are  extruded.  If  the  egg  is  fertilized  it  gives  rise  to 
a  female  (queen  or  worker),  but  if  the  egg  is  unfertilized  it  produces 
a  male  (drone).  The  male  has  only  the  single  set  of  chromosomes. 
One  set  of  chromosomes,  then,  produces  a  male,  two  a  female;  but 
whether  sex  is  the  result  of  special  genes  carried  by  one  or  two  sex 
chromosomes  has  not  been  determined.  Corresponding  with  the 
single  (haploid)  number  of  chromosomes  in  the  male,  the  spermato- 
genesis shows  certain  special  features.  The  preparation  for  the  first 
division  takes  place,  and  only  a  small  non-nucleated  piece  of  proto- 
plasm is  pinched  off  at  one  pole  of  the  cytoplasmic  spindle.  Prepara- 
tion for  a  second  division  follows  and  the  chromosomes  separate  into 
two  groups,  but  the  cytoplasmic  division  is  very  unequal  and  only 
one  of  the  nucleated  cells  that  results  becomes  a  functional  spermato- 
zoon. That  at  the  second  division  an  equational  division  of  the 
chromosomes  occurs  is  probable,  for  in  the  closely  related  wasps  the 
second  division  takes  place  normally  (according  to  Mark  and  Cope- 
land)  and  two  spermatozoa  are  formed,  each  wdth  the  single  number 
of  chromosomes.  Since  in  the  male  the  haploid  number  of  chromo- 
somes must  be  supposed  to  be  present,  it  might  have  been  anticipated 
that  his  nuclei  w^ould  be  half  the  size  of  those  in  the  corresponding 
parts  of  the  female,  as  happens  in  the  sea-urchin  egg  when  haploid 
and  diploid  nuclei  occur  in  different  regions  of  the  same  embryo.  An 
examination  of  this  relation  by  Miss  M.  Oehninger  has  show^n,  how- 
ever, that  no  such  difference  is  present;  hence  what  might  have  been 
a  means  of  determining  the  constitution  of  the  male  and  female  parts 
of  the  gynandromorph  is  lacking. 

Von  Siebold  found  the  male  and  female  characters  combined  in 
many  different  ways  in  his  gynandromorph  bees,  much  as  we  find  them 
in  Drosophila.  In  some  cases  one  side  was  male,  the  other  female; 
or  the  anterior  end  might  be  like  that  of  one  sex  and  the  posterior 
like  that  of  the  other;  sometimes  different  regions  of  the  same  organ, 
such  as  an  eye,  leg,  or  antenna,  might  contain  both  male  and  female 
regions.  The  normal  worker  has  a  sting,  the  male  is  without  this 
organ.  In  the  gynandromorphs  the  sting  was  present  if  the  abdomen 
was  like  that  of  the  worker,  but  absent  when  the  abdomen  was  hke 
that  of  the  male.  No  definite  relation  was  found  between  the  super- 
ficial characters  of  the  abdomen  and  its  contained  gonad.  Testis 
and  ovary  might  even  be  combined  into  one  organ.  Externally  the  male 
genital  apparatus  might  be  present  and  ovaries  and  oviducts  exist  inside. 


76 


THE    ORIGIN   OF   GYNANDROMORPHS. 


Von  Siebold  attempted  to  account  for  the  gynandromorphs  by  the 
assumption  that  an  insufficient  number  of  sperm  entered  the  egg, 
so  that  part  of  it  lacked  sufficient  quantities  of  the  male  element. 
It  is  true  that  recent  discoveries  (Nachtsheim)  have  shown  that 
more  than  one  spermatozoon  does  usually  enter  the  egg,  but  we  can 
not  explain  the  results  on  this  basis  in  the  sense  intended  by  von 
Siebold.  Von  Siebold  gave  no  clear  account  of  the  varietal  character 
of  the  male  and  female  parts  of  the  gynandromorph  (see  Boveri, 
p.  286),  and  in  consequence  it  is  not  possible  from  his  account  to 
determine  whether  the  male  parts  were  like  those  of  the  Italian  or 
German  parent.  It  remained  for  Boveri,  after  47  years,  to  attempt 
to  make  out,  from  the  alcoholic  remains  of  some  of  von  Siebold's  bees, 
the  character  of  these  parts. 

In  order  to  better  present  here  the  conditions  in  the  gynandro- 
morph, copies  of  Mehling's  figures  of  the  head  of  the  normal  bees 
are  reproduced  in  text-figure  64,  a,  of  the  drone,  h  of  the  worker,  and  c 


Text-figure  64. 

of  one  of  the  gynandromorphs  of  von  Siebold's  bees.  The  com- 
pound eyes  of  the  drone  are  enormous  in  comparison  with  those  of 
the  worker,  and  meet  above  at  the  top  of  the  head.  The  three  simple 
eyes  are,  in  the  drone,  forward  near  the  middle  of  the  ''face",  but  on 
the  top  of  the  head  in  the  worker.  In  the  latter  there  is  a  tuft  of  long 
hair  on  the  top  of  the  head.  In  the  gynandromorph  copied  in  figure  64 
the  same  approximate  differences  in  the  size  of  the  compound  eyes  is 
seen  on  the  male  and  on  the  female  side.  Two  of  the  simple  eyes  on 
the  drone  side  are  low  down,  while  the  third,  on  the  worker  side,  is 
at  the  top  of  the  head,  where  a  small  tuft  of  hair  is  also  present.  The 
face  of  the  worker  is  darker  than  that  of  the  male,  and  the  same  difference 
in  color  is  seen  in  the  gynandromorph.  The  antennae  are  larger  in 
the  drone,  and  this  difference,  too,  is  manifest  in  the  gynandromorph, 
as  is  also  the  difference  in  size  of  the  jaws.     Many  other  differences 


THE    ORIGIN    OF    GYNANDROMORPHS.  77 

as  striking  as  these  are  found  in  other  parts  of  the  body  and  come  out 
equally  well  in  the  gynandromorph.  Miss  Alehling  shows  that  the 
male  and  female  parts  may  sometimes,  however,  be  so  intimately 
combined  that  a  particular  organ,  such  as  a  leg,  may  seem,  on  super- 
ficial examination,  to  be  a  blend  of  the  two.  A  minute  examination 
shows,  however,  as  a  rule,  that  such  an  organ  is  a  piecework  or  mosaic 
of  male  and  female  characters. 

It  will  be  recalled  that  Boveri's  hjTDothesis  appealed  to  the  phenom- 
enon of  partial  fertilization.  A  belated  sperm,  sometimes  failing  to 
fuse  with  the  egg  nucleus  before  the  latter  divides,  comes  to  combine 
with  only  one  half  of  the  latter.  As  a  result,  one  of  the  first  two 
segmentation  nuclei  contains  only  the  maternal  daughter  nucleus, 
the  other  the  combined  maternal  daughter  nucleus  and  the  entire 
sperm  nucleus.  The  application  of  the  results  to  the  gynandromorph 
bees  is  obvious.  If  these  are  due  to  partial  fertilization,  then  we 
should  expect  the  male  side  to  be  like  that  of  the  mother's  race — the 
Italian  bee — because  its  haploid  chromosome  group  came  directly 
from  the  Italian  mother's  egg.  Vice  versa,  the  female  side  should 
show  hybrid  characters,  or  the  Italian  character  if  the  Italian  race 
dominates  completely  the  German  race.  If  the  latter,  both  sides 
would  then  be  alike  and  racially  indistinguishable.  Morgan's  sug- 
gestion of  polyspermy  leads  to  the  following  explanation:  If  under 
unusual  circumstances  one  (or  more)  of  the  spermatozoa  should 
develop,  the  parts  supplied  by  its  nuclei  would  be  haploid,  hence  male, 
while  the  other  parts  resulting  from  the  combined  nuclei  would  be 
female.  The  expected  characters  of  the  two  parts  of  the  gynandro- 
morph would  be  the  reverse  of  those  called  for  by  Boveri's  hypothesis, 
for  the  male  parts  should  be  paternal  on  Morgan's  \dew,  maternal 
on  Boveri's.  The  decision  lies,  therefore,  in  the  character  of  the  male 
parts  of  the  gynandromorph.  Boveri  examined  von  Siebold's  bees, 
some  of  which  had  been  preserved  in  Munich,  in  order  to  get  an 
answer  to  this  problem,  and  reached  the  conclusion  that  the  male 
parts  are  maternal.  Hence  the  answer  was  in  favor  of  his  own  hypo- 
tliesis.  We  may  now  proceed  to  examine  this  evidence  in  detail  and 
then  see  whether  the  hypothesis  of  chromosome  elimination  may  not 
fit  the  facts  as  well  as  either  of  the  alternative  views. 

After  nearly  50  years  in  alcohol  the  Eugster  gynandromorphs  had 
lost  so  much  of  their  color  that  a  comparison  with  the  racial  pigmenta- 
tion as  seen  in  the  living  bees  was  impossible.  Only  after  extracting 
the  superficial  pigment  and  dissolving  away  the  external  parts  of  fresh 
individuals  of  the  two  parental  races  was  it  possible  for  Boveri  to 
make  any  reliable  comparisons.  Even  then  only  a  few  individuals 
were  available,  because  "an  vielen  Exemplaren  das  Abdomen  nahezu 
farblos  ist."  Boveri  confines  his  account  to  four  specimens  and  in 
these  takes  only  the  head  and  abdomen  into  account. 


78  THE    ORIGIN   OF   GYNANDROMORPHS. 

The  difference  in  the  coloration  of  the  heads  of  the  males  of  mellifica 
and  ligustica  is  in  the  prepared  skeleton  very  slight,  but  Boveri  thinks 
that  the  male  parts  of  the  gynandromorphs'  heads  are  colored  more 
like  the  same  parts  of  the  ligustica.  Their  abdomens  show  more  strik- 
ing differences,  not  only  in  the  relative  amount  of  deeper  pigment,  but 
in  the  pigment  pattern  as  well.  A  comparison  of  the  distribution  of 
the  pigment  of  the  male  side  of  the  gynandromorph  with  the  sides  of 
the  males  of  the  two  races  seemed  to  him  to  show  again  that  the  closer 
match  is  with,  the  ligustica  type  of  pigmentation.  The  deep  pigmenta- 
tion of  the  ventral  surfaces  of  the  two  races,  especially  in  the  males, 
offers  more  positive  differences,  especially  as  to  color-pattern.  The 
comparison  shows  here  that  when  the  abdomen  of  the  gynandromorph 
is  male  its  deeper  color  is  more  like  the  ligustica  type,  except  when  in 
places  the  male  parts  include  or  are  replaced  by  female  areas.  Despite 
the  fact  that  the  comparisons  that  Boveri  gives  rest  on  rather  a  slender 
foundation,  the  evidence,  so  far  as  it  goes,  is  clearly  in  favor  of  his 
interpretation  of  the  nature  of  the  male  parts  of  the  gynandromorphs. 
The  well-known  accuracy  and  carefulness  of  Boveri's  work  prejudices 
one  strongly  in  favor  of  his  opinion. 

Boveri's  evidence  would  seem,  then,  to  settle  the  case  in  his  favor 
were  it  not  that  another  account  appeared  just  before  the  publication 
of  Boveri's  paper  (which  he  cites  at  length),  based  on  observation  of 
living^  material— an  account  that  leads  to  exactly  the  opposite  con- 
clusion from  that  reached  by  Boveri.  Engelhardt  described  (1914) 
some  gynandromorphs  in  which  he  stated  that  the  male  parts  are  dark 
brown  (paternal)  and  the  female  reddish  yellow  (maternal).  These 
gynandromorphs  came  from  an  Italian  mother  and  a  father  belonging 
to  a  local  (einheimischen)  race.  The  case  is  parallel  to  the  Eugster 
bees,  and  the  only  room  left  for  doubt  is  the  nature  of  the  local  race. 
The  local  race  of  the  northern  Caucasus,  whence  the  evidence  comes, 
is  probably,  according  to  Boveri,  Apis  mellifica  ramipes.  Here  there 
is  some  more  recent  evidence  that  is  important.  Quinn  has  shown 
(1916)  that  when  a  yellow  Italian  queen  is  crossed  to  a  gray  drone  of 
the  Caucasus  race  the  daughters  (hybrids)  and  the  drones  are  yellow 
like  the  Italian.  This  result  indicates  that  the  material  used  by  von 
Engelhardt  was  suitable  for  giving  differences  in  the  gynandromorphs 
that  could  be  used  to  distinguish  the  character  of  the  male  parts. 
It  follows  that  von  Engelhardt's  results  support  Morgan's  and  not 
Boveri's  hypothesis. 

Since  these  views  deal  with  paternal  or  maternal  nuclei  as  wholes, 
it  is  immaterial  whether  the  factor  differences  are  carried  by  the  sex 
chromosomes  or  by  some  other  chromosomes,  but  when  the  third  view 
comes  up  for  consideration  the  question  of  which  chromosome  pair 
is  involved  is  of  vital  moment.     Let  us  see,  then,  how  the  hypothesis 

^  Or  at  least  not  alcoholic. 


THE    ORIGIN    OF    GYNANDROMORPHS.  79 

of  chromosomal  elimination  applies  to  von  Siebold's  and  von  Enf];cl- 
hardt's  gjmandromorphs. 

In  the  first  place,  it  is  important  to  understand  that  there  is  no 
conclusive  evidence  that  the  racial  difference  here  involved  lias 
anything  to  do  with  one  particular  chromosome,  or  even  with  the 
sex  chromosome.  In  bees  the  mother  transmits  her  characters 
directly  to  her  sons,  as  is  the  case  in  sex-linked  inheritance  of  the 
Drosophila  type,  but  in  bees  this  form  of  inheritance  is  obviously  due 
to  the  fact  that  the  male  develops  directly  from  the  unfertilized  egg, 
hence  must  inherit  all  the  maternal  characters,  whether  in  the  sex 
chromosome  or  in  the  autosomes.  The  special  sex  differences  are, 
of  course,  due  to  whatever  it  is  that  makes  the  egg  a  male  or  a  female. 
In  cases  where  the  queen  is  heterozygous  she  may  produce  two  kinds 
of  sons,  which  is  expected  if  the  two  races  differ  in  one  Mendelian 
gene,^  but  this  would  hold  whether  this  pair  of  genes  is  autosomal  or 
in  a  pair  of  sex  chromosomes.  If  the  two  races  differ  in  more  than  one 
pair  of  genes,  more  than  two  kinds  of  males  are  expected.  The  clearest 
evidence  that  we  have  in  regard  to  what  a  hybrid  queen  produces  is 
furnished  by  the  recent  work  of  Newell  (1914)  and  Quinn  (1916). 
Newell  crossed  a  yellow  Italian  queen  bee  to  a  gray  Carniolan  drone. 
The  daughters  were  yellow  like  the  Italian,  showing  the  dominance 
of  that  color.  In  the  reciprocal  cross,  Carniolan  female  by  Italian 
drone,  the  daughters  were  also  yellow,  but  not  as  completely  so  as  in 
the  last.  Whether  this  is  due  to  modifying  factors  of  some  kind  is  not 
known.  Quinn,  as  stated  above,  used  Italian  and  Caucasus  races, 
crossing  both  ways,  and  in  both  the  daughters  were  the  same,  viz, 
3"ellow  like  the  dominant  Italian  race.  He  also  found  that  the  Fi 
daughters  gave  two  kinds  of  drones  and  two  only,  which  indicates  that 
the  factor  difference  is  carried  by  a  pair  of  chromosomes,  but  this  evi- 
dence alone  does  not  show  that  the  pair  is  the  pair  of  sex  chromosomes, 
for  any  other  pair  would  give  in  the  bee  the  same  result.  However, 
when  taken  in  connection  with  the  gynandromorph  results,  the  evidence 
becomes  somewhat  stronger  that  sex  chromosomes  are  involved. 

What,  then,  is  the  expectation  on  the  elimination  view?  It  is  at 
once  apparent  that  the  elimination  must  involve  a  sex  chromosome, 
for,  otherwise,  there  is  no  reason  to  suppose  that  an  autosomal  dif- 
ference would  at  the  same  time  be  associated  with  a  difference  in  sex. 
In  other  words,  the  elimination  hypothesis  can  apply  here  only  if  the 
chromosome  that  determines  sex  is  the  same  chromosome  that  causes 
this  racial  difference. 

Elimination  of  one  of  the  sex  chromosomes  that  carries  the  factor 
for  mellifica  would  produce  a  cell  containing  only  the  ligustica-heanng 
chromosome,  and  all  parts  descending  from  that  cell  would  be  both 

^  It  has  been  pointed  out  that  the  exceptions  recorded  by  Cu6not  may  be  due  to  dronea  comiDg 
from  hybrid  workers.     (Morgan,  19()9a,  Am.  Nat.,  XLIII.) 


80  THE    ORIGIN    OF   GYNANDROMORPHS. 

male  and  ligustica.  This  is  the  result  which  Boveri  thinks  is  shown 
by  the  Eugster  gynandromorphs.  Conversely,  if  the  ligustica  chromo- 
some were  lost,  all  parts  containing  the  descendants  of  this  nucleus 
would  be  male  and  mellijica.  This  is  the  result  that  von  Engelhardt 
claims  to  have  found  in  his  gynandromorphs.  Thus  both  results  are 
expected  on  the  hypothesis  of  chromosomal  elimination ;  each  is  equally 
possible.  Boveri's  hypothesis  of  partial  fertilization  explains  only 
one  case;  Morgan's  former  view  of  sperm-nuclear  development  will 
explain  only  the  other;  the  hypothesis  of  elimination  will  explain  both, 
and  for  this  reason  is  at  present  to  be  preferred.  Moreover,  since  it  is 
demonstrably  the  way  in  which  gynandromorphs  are  produced  in  Droso- 
phila,  this  hypothesis  is  more  general  than  either  of  the  earlier  views. 

There  is  a  further  implication  in  these  cases  of  hybrid  gynandro- 
morphs in  bees  that  can  now  be  cleared  up.  The  female  parts  of  the 
gynandromorph  are  of  hybrid  origin.  On  any  view,  therefore,  these 
parts  are  expected  to  be  not  necessarily  like  the  mother  (unless  her 
character  is  the  dominant  one), but  hybrid.  If  the  mellijica  color  is 
dominant,  then  on  Boveri's  views  the  female  side  of  the  gynandro- 
morph should  be  mellijica,  but  according  to  Newell  the  Italian  yellow 
color  is  dominant,  hence  in  half  the  Eugster  gynandromorphs  the  male 
and  female  sides  should  have  the  same  color.  Perhaps  this  accounts 
for  the  astonishing  failure  on  the  part  of  von  Siebold  to  mention  the 
color  differences  in  his  gynandromorphs,  since  the  superficial  (the 
racial  differences  in  color)  color  was  often  the  same  on  the  two  sides. 
If  this  is  the  real  situation,  Boveri  must  have  worked  with  a  deeper 
color  difference,  one  that  is  ordinarily  not  apparent.  It  is  doubtful 
from  his  description  whether  he  could  determine  if  the  female  parts 
were  mellijica  or  Italian  or  intermediate.  He  recognizes  the  difficulty, 
for  he  refrains  from  making  any  comparison  between  the  female  parts 
and  those  of  the  hybrid  workers,  but  so  far  as  he  suggests  any  com- 
parison it  is  with  the  pure  mellijica  type. 

In  von  Engelhardt's  case  the  male  parts  are  described  as  darker, 
hence  more  like  mellijica,  while  the  female  parts  are  described  as 
lighter.  Since  Quinn  shows  that  the  yellow  (lighter)  color  is  dominant, 
the  two  sides  should  be  different,  hence  the  fact  strongly  supports 
von  Engelhardt's  interpretation.  In  fact,  I  do  not  see  how  we  can 
avoid  the  conclusion  that  von  Engelhardt's  results  are  supported  by 
much  better  evidence  than  are  Boveri's  own,  if  any  such  comparison 
must  be  made.  Both  are  probably  right,  and  the  theory  of  chromo- 
somal elimination  not  only  accounts  for  both,  but  on  that  theory  both 
kinds  of  results  are  expected. 

If,  as  here  suggested,  both  the  Eugster  and  the  von  Engelhardt 
gynandromorphs  are  due  to  chromosomal  elimination,  it  follows  that 
there  must  have  been  also  other  gynandromorphs  present  that  were 
not  color-hybrids,  but  show  the  dominant  color  both  in  male  and 
in  female  regions.     In  fact,  these  must  have  been  as  conmaon  as  the 


THE    ORIGIN   OF   GYNANDROMORPHS. 


81 


hybrid  types.  How  can  we  account  for  this  absence  of  all  reference 
to  such  cases?  It  is  to  be  recalled  that  Boveri  actually  studied  only 
a  few  cases,  stating  that  others  were  not  sufficiently  well  preserved  to 
show  the  hybrid  differences  between  the  parts.  It  should  also  not  be 
overlooked  that  the  more  striking  differences  in  color  in  the  living 
hybrid  bees  would  draw  attention  to  these,  while  gynandromorphs 
colored  alike  on  both  sides  would  be  overlooked.  A  census  of  all  the 
gynandromorphs  occurring  under  such  conditions  is  necessary  before 
it  will  be  safe  to  conclude  that  these  reciprocal  cases  did  not  occur. 
Boveri  was,  of  course,  only  concerned  w4th  such  cases  as  showed  the 
maternal  character  of  the  male  parts,  and  as  such  are  expected  in 
half  of  the  cases,  it  would  be  natural  to  select  these  as  illustrations  of 
his  theory.  Until  another  survey  of  the  entire  output  in  such  cases 
is  recorded  this  test  of  the  correctness  of  the  elimination  hypothesis 
can  not  be  applied. 

Wheeler  (1910)  has  described  a  beautiful  case  of  gynandromorphism 
in  a  mutillid  wasp.  The  male  half  of  the  body  is  black  and  winged 
like  the  male,  while  the  female  half  is  rich  red  and  wingless. 

The  ants  are  closely  related  to  the  bees,  and  sex  determination 
appears  to  be  in  general  the  same,  although  there  are  some  cases, 
apparently  well  authenticated,  where  unfertilized  eggs  have  produced 
queens  and  workers  as  well  as  males.  There  were,  prior  to  1903,  17 
cases  of  gynandromorphs  known  in  ants  which  were  brought  together 
by  Wheeler,  to  which  he  added,  in  1914,  6  new  cases.  These  show  the 
same  relations  of  parts  seen  in  bees  and  call  for  no  further  comment. 
None  were  hybrids  and  furnish,  therefore,  no  evidence  for  causal 
flimi.1  vsis 

GYNANDROMORPHS  IN  LEPIDOPTERA. 

The  group  of  Lepidoptera,  including  butterflies  and  moths,  has 
furnished  more  gynandromorphs  than  any  other  group  of  animals, 
even  more  than  the  single  species  Drosophila  melanogaster,  if  all  butter- 
flies and  moths  are  taken  together.  It  has  been  estimated  that  at 
least  1,000  cases  of  g^niandromorphs  have  been  recorded  for  this 
group. ^     Whether  they  are  actually  more  frequent  than  in  other  insects 

^Wenke  (1906),  summing  up  Schultz's  reviews  of  1898-1899,   states  that  the  909  g>-nandro- 
morphs  (and  hermaphrodites)  brought  together  by  the  latter  fall  within  the  following  species: 


Species. 

Indi- 
viduals. 

Species. 

Indi- 
viduals. 

Smerinthus  populi 

Saturnia  pavonia 

Rhodocera  rhamni 

67 
51 
40 
34 
33 
33 
29 

Lycsena  icarus 

28 
24 
23 
10 

ir> 

13 

Bombyx  quercus 

Ocneria  dispar 

Rupalus  piniarius 

Rhodocera  cleopatra 

Anthocharis  cardamines .  .  . 

Argj'nnis  pai)hia 

Lasiocampa  pini 

Lasiocamjia  fasoiatella  .  .  . 
Limcnitis  populi 

82 


THE    ORIGIN   OF   GYNANDROMORPHS. 


or  whether,  owing  to  the  striking  character  of  their  wings,  they  have 
more  often  attracted  attention,  is  perhaps  open  to  question.  The  dif- 
ferences between  the  coloration  of  the  males  and  females  in  some 
species  would  at  once  arrest  attention.  On  the  other  hand,  in  certain 
species  and  in  certain  hybrid  combinations  the  number  of  gynandro- 
morphs  is  so  great  that  there  can  be  little  doubt  that  their  occurrence 
here  is  directly  related  to  the  specific  or  to  the  hybrid  nature  of  the 
insects. 

Eleven  more  gynandromorphs  of  Argynnis  paphia  added  by  Wenke 
brings  the  total  to  nearly  1,000. 

In  regard  to  the  chromosomal  background,  the  situation  is  the 
converse  of  that  in  Drosophila  and  in  nearly  all  other  insects.  The 
male  has  two  sex  chromosomes  (text-fig.  65),  which  may  we  call  ZZ, 
and  the  female  one,  Z,  and  another  called  W,  corresponding  to  the 
Y  of  Drosophila.  The  genetic  evidence  in  the  case  of  Abraxas  makes 
this  view  highly  probable,  and  Seller  has  shown  in  another  moth  that 
there  is,  in  fact,  such  a  chro- 
mosomal difference  between  wz  zz 
the  female  and  the  male. 
As  has  been  stated,  in  Dro- 
sophila the  female  combina- 
tion XX  is  the  basis  for  most 
of  the  gynandromorphs  be- 
cause the  combination  al- 
lows, through  the  elimina- 
tion of  one  of  the  X's,  the 
formation  of  parts  with  one 
X  which  is  male.  By  anal- 
ogy we  should  expect  in  Lepidoptera  that  the  male  combination  ZZ 
would  furnish  the  basis  for  the  gynandromorphs  of  this  group,  since 
through  elimination  of  one  Z  the  female  condition  w^ould  arise. 

The  most  interesting  case  in  the  Lepidoptera  is  tliat  of  a  hybrid 
gynandromorph  in  the  silkworm  moth,  because  here  we  know  the 
genetic  relation  of  the  factors  involved.  Toyama  obtained  two  bilateral 
gynandromorph  caterpillars  whose  mother  belonged  to  a  race  with  a 
striped  ''zebra"  pattern  in  the  caterpillars  and  whose  father  belonged 
to  a  race  with  unicolorous  white  larvae.  Experiments  show  that  in 
general  zebra  pattern  is  dominant  to  white.  Neither  is  sex-linked. 
The  left  female  side  of  the  gynandromorph  caterpillar  was  zebra,  the 
right  side  white.  If  we  attempt  to  analyze  this  case  on  the  basis  of 
Boveri's  or  of  Morgan's  earlier  views — views  based  on  the  assumption 
that  one  or  two  nuclei  determine  male  and  female  respectively — and 
assuming  that,  as  in  the  bees,  the  male  parts  have  one  nucleus 
and  the  female  parts  the  combined  nuclei,  then  the  result  confirms 
Morgan's  view  and  not  Boveri's.     But  this  interpretation  does  not 


wz 


Text-figure  65. 


THE    ORIGIN    OF   GYNANDROMORPHS. 


83 


get  to  the  bottom  of  the  situation  in  the  light  of  more  recent  work, 
for  in  moths  it  now  seems  probable  that  one  Z  sex  chromosome 
(the  equivalent  in  part  of  one  nucleus)  makes  a  female  and  two  a  male. 
There  are,  then,  two  kinds  of  ripe  eggs,  one  with,  the  other  without,  a 
Z,  and  one  kind  of  sperm,  which  is  Z-bearing.  There  are  six  possi- 
bilities to  be  considered  (see  diagrams,  text-figs.  66,  67,  68). 

(1)  On  Boveri's  view  (text-fig.  66,  1),  if  an  egg  with  a  W  was  the 
kind  fertilized,  then  one  half  of  the  maternal  segmentation  nucleus 
should  have  no  Z  and  would  probably  not  develop,  while  the  other 


Text-figure  66. 

half  of  the  egg  nucleus,  that  united  with  the  sperm  nucleus,  should 
have  one  Z  and  be  both  female  and  white.  This  explanation  fails  to 
account  for  the  male  sex  of  the  side  supposed  to  be  without  a  Z  and  for 
the  presence  of  zebra  on  that  side. 

(la)  On  Boveri's  view  (text-fig.  66,  la),  if  an  egg  with  a  Z  were 
fertilized  by  a  sperm  (bearing  Z),then  both  the  male  and  female  sides 
should  be  zebra,  which  is  contrary  to  evidence. 


Text-figure  67. 


(2)  On  Morgan's  earlier  view  (text-fig.  67,  2),  an  egg  trith  a  W 
fertilized  by  a  sperm  (bearing  Z)  should  give  female  parts  from  the 
combined  nuclei  which  would  be  white.  The  sperm  nucleus  alone 
would  also  give  female  parts  which  would  be  plain.  The  result  is  a 
mosaic,  but  not  a  gynandromorph. 

(2a)  On  Morgan's  view  (text-fig.  67,  2a),  if  an  egg  ivith  a  Z  had 
been  fertilized  by  a  Z  sperm,  all  male  parts  (ZZ)  should  be  zebra. 
The  female  parts  would  be  plain,  which  is  again  contrary  to  fact. 


84 


THE    ORIGIN   OF   GYNANDROMORPHS. 


(3)  On  the  elimination  hypothesis  (text-fig.  68,  3),  an  egg  with 
a  W  fertilized  by  a  sperm  (Z-bearing)  should  produce  a  female  (ZW). 
This  gives  no  chance  to  produce  a  male  side  (ZZ)  by  ordinary  elimina- 
tion. If  by  somatic  non-disjunction  (ZZ  or  no  Z)  it  is  not  evident  that 
the  no-Z  part  would  develop,  and  if  it  did,  why  it  should  be  plain. 

(3a)  If  an  egg  with  a  Z  had  been  fertilized  by  a  Z  sperm  (text-fig. 
68,  Sa),  a  male  (ZZ)  would  result  from  which,  by  elimination  of  a  Z 
chromosome  bearing  the  white  gene,  would  produce  female  parts  that 
are  zebra  and  male  parts  that  are  also  zebra,  which  is  contrary  to  the 
actual  conditions  in  the  gynandromorph.  If  the  other  chromosome 
should  be  eliminated,  viz,  the  one  bearing  the  zebra  gene,  then  the 
male  part  would  be  zebra  and  the  female  part  would  be  plain. 

It  is  evident  that  this  case  can  not  be  explained  in  any  of  these 
ways,  even  though  it  be  assumed  that  the  color-factors  are  carried  by 
the  sex  chromosomes.    And  if  we  do  treat  the  color-factors  as  sex- 


Text-figure  68. 

linked,  then  they  can  not  be  the  same  zebra-white  pair  of  factors 
described  by  Toyama  in  other  crosses  which  are  clearly  not  sex- 
linked.  To  apply  the  above  view  tactily  takes  for  granted  that  the 
zebra-white  pair  is  not  the  same  pair  referred  to  in  other  crosses.  If  it 
is  not,  then  we  are  not  obliged  to  assume  that  zebra  is  dominant  to  plain. 
If  plain  is  assumed  to  be  dominant  over  zebra,  the  gynandromorph  can 
be  accounted  for  by  Boveri's  hypothesis  or  by  elimination.  Possibly  one 
might  try  to  find  an  excuse  for  such  an  evasion  by  pointing  out  that 
Toyama  states  that  the  two  gynandromorphs  appeared  in  a  cross 
between  a  striped  French  race  with  yellow  cocoons  and  a  common 
Japanese  race  with  white  cocoons,  and  that  this  is  not  the  same  cross 
as  that  which  he  described  in  the  body  of  his  paper,  where  he  states 
that  the  striped  race  had  white  cocoons.  On  the  other  hand,  both 
Coutagne  and  Kellogg,  according  to  Tanaka,  have  found  that  striped 
is  dominant  to  plain,  and  although  I  can  not  find  that  they  have 
made  exactly  the  same  cross  as  that  which  yielded  the  gynandromorph, 
nevertheless  the  cumulative  evidence  is  strongly  in  favor  of  the  view 
that  zebra  is  both  dominant  and  not  sex-linked.     It  is  clear,  then,  that 


THE    ORIGIN    OF   GYNANDROMORPHS.  85 

we  must  search  for  some  other  kind  of  explanntion  for  Toyama's 
gynandromorphs.  Fortunately,  Doncaster's  observation  on  the  eggs 
of  a  race  of  Abraxas  gives  us  a  clue  to  an  explanation.  Doncaster, 
as  stated  on  page  20,  found  occasionally  an  egg  containing  two  nuclei, 
each  nucleus  being  about  to  be  fertilized  by  a  separate  spermatozoon. 
Now,  if  in  Toyama's  case  the  zebra  mother  was  heterozygous,  one  of 
the  two  nuclei  in  question  might  contain  a  Z  chromosome  and  an  auto- 
some with  a  gene  for  plain  color  (Z  and  white),  while  the  other  nucleus 
might  contain  a  W  chromosome  and  an  autosomal  gene  for  zebra  (W 
and  zebra).  Two  sperms  of  the  father,  each  with  a  white-bearing 
autosome,  each  fertilizing  one  egg  nucleus,  would  give  a  white  male 
side  (Z,  white;  Z,  white)  and  a  female  zebra  side  (W,  white;  Z,  zebra). 
This  seems  the  most  probable  interpretation. 

There  is  still  another  possible  explanation  of  Toyama's  gynandro- 
morphs, viz,  that  the  male  parts  have  come  from  the  fusion  of  nuclei 
derived  from  two  (or  more)  spermatozoa.  Pairs  of  such  nuclei  would 
give  ZZ  cells  that  would  be  male  and  paternal.  It  is  true  that  Herlandt 
and  Brachet  find  in  the  frog  that  sperm  nuclei  do  not  fuse  in  the  egg, 
but  they  attribute  this  to  the  cy tasters  that  keep  them  apart.  If 
in  the  moth  (and  bee?)  the  cystasters  are  less  well  developed,  con- 
tiguous nuclei  might  sometimes  fuse. 

Another  moth.  Abraxas,  has  been  extensively  used  by  Raynor  and 
Doncaster  in  genetic  experiments.  The  characters  in  question  {gros- 
sulariata  versus  lacticolor)  show  sex-linked  inheritance  and  should  furnish 
interesting  evidence  as  to  the  nature  of  gynandromorphs  in  moths. 

Quite  recently  Doncaster  has  reported  two  gynandromorphs  of 
Abraxas  that  arose  in  a  cross  between  these  two  types.  The  first 
case  arose  in  a  cross  between  grossulariata  female  by  lacticolor  male. 
The  normal  expectation  for  this  cross  is:  grossulariata  males  and 
lacticolor  females.  There  were  produced  24  lacticolor  females,  no 
grossulariata  males,  and  one  gynandromorph  that  was  lacticolor  but 
mixed  in  certain  parts.  The  absence  of  males  is  apparently  con- 
nected with  an  exceptional  chromosomal  condition  in  this  family 
(viz,  55  chromosomal  line)  of  such  a  sort  that  all  the  fertilized  eggs 
lacked  a  chromosome,  the  single  Z  passing  out  into  the  polar  bodies 
in  all  or  nearly  all  cases.  The  main  characters  of  this  gynandromorph 
are  "the  right  antenna  is  male,  the  left  female,  and  the  frenulum  of 
the  left  wing  is  of  the  male  type  and  well  developed,  that  of  the  right 
male  but  imperfect.  In  the  external  genitalia  the  chief  points  are 
that  the  uncus,  anus,  and  ovipositor  are  each  divided;  the  right  vulva 
is  not  unlike  that  of  a  normal  male,  the  left  side  is  abnormal  and  has 
attached  to  it  a  second  anus  and  half  of  the  ovipositor,"  etc.  Don- 
caster sums  up  the  chief  peculiarities  of  this  moth  as  follows: 

"(1)  That  though  predominantly  male,  it  has  the  lacticolor  character  which, 
from  its  parentage,  should  be  confined  to  females;  (2)  throughout  the  body 


86  THE    ORIGIN    OF   GYNANDROMORPHS. 

the  right  side  is  male,  the  left  imperfectly  developed,  a  tendency  towards  the 

female  type The  internal  genital  organs  were,  as  far  as  is  known, 

imperfectly  developed  male  organs." 

A  theoretical  explanation  of  the  case,  based  on  the  chromosomal 
peculiarities  of  the  line,  is  as  follows :  Since  practically  all  eggs  had  but 
one  Z  chromosome  before  polar-body  extrusion  and  lost  it  at  their 
formation,  few  males  arise  as  Doncaster  has  shown,  and  even  if  Z 
should  exceptionally  remain  in  a  ripe  egg  it  would  carry  the  gene  for 
grossulariata;  hence  any  male  coming  from  it  would  be  grossulariata. 
Only  then  by  the  sperm  bringing  two  Z's  into  a  Z-less  egg  could  a 
lacticolor  male  arise.  Such  an  abnormal  sperm  could  arise  in  any 
male  by  primary  non-disjunction,  or  by  secondary  non-disjunction 
from  a  ZZW  male,  i.  e.,  by  the  two  Z's  of  the  spermatogonia  both 
passing  to  the  same  pole  at  one  of  the  maturation  divisions.  If  this 
happens,  a  lacticolor  male  is  expected.  The  appearance  of  femaleness 
in  certain  parts  of  the  left  side  must,  then,  be  referred  to  an  elimination 
of  one  of  the  Z's  at  some  early  division. 

Doncaster's  second  case  can  be  explained  as  a  simple  case  of  chromo- 
somal elimination.  A  grossulariata  female,  by  lacticolor  male,  gave 
11  grossulariata  males  -[-11  lacticolor  females  -\-  1  gynandromorph 
whose  anterior  parts  are  male  (including  the  wings  to  some  extent), 
and  whose  posterior  parts  are  female.  Here  the  normal  proportion 
of  males  to  females,  and  the  expected  distribution  of  color  to  them, 
shows  that  the  female  "was  normal  as  to  her  chromosomes.  If  we 
assume,  then,  that  a  Z-bearing  egg  was  fertilized  by  a  normal  Z-bearing 
sperm,  the  result  should  be  a  normal  grossulariata  female  heterozygous 
for  lacticolor.  Elimination  of  one  of  the  paternal  Z's  would  give  a 
grossulariata  male  in  the  anterior  region  coming  from  the  ZZ  nuclei 
and  a  grossulariata  female  posterior  part  coming  from  the  single  Z 
nucleus.  The  second  case  is  comparable  in  every  way  with  the  cases 
of  Drosophila  and  allows  an  extension  of  the  theory  of  chromosomal 
elimination  to  the  group  of  moths,  in  line  with  the  other  critical  cases 
described  above.  Doncaster's  first  case  must  also  appeal  in  part  to 
the  same  hypothesis,  but  it  is  more  complicated,  since  another 
exceptional  phenomenon  must  have  first  occurred.  This  first  process 
gives  a  lacticolor  male  when  a  grossulariata  male  or  no  males  at  all  are 
expected.  It  is  only  that  elimination  later  happened  to  take  place 
in  this  individual  that  it  comes  to  be  considered  in  this  connection. 
In  other  words,  there  is  no  necessary  connection  between  the  two 
events,  so  that  the  non-disjunction  phenomenon  does  not  in  reality 
complicate  the  elimination  explanation.  The  two  are  quite  inde- 
pendent. It  should  be  pointed  out  that  such  exceptional  males  due  to 
non-disjunction  are  known  to  occur  in  Abraxas. 

Another  gynandromorph  in  Abraxas  (Tutt.  1897)  involves  varieties 
A.  ab.  suffusa  and  A.  ab.  obscura.     Since  the  genetic  relation  of  these 


THE   ORIGIN   OF   GYNANDROMORPHS.  87 

characters  to  the  type  grossulariata  are  not  known,  nor  the  parentage 
of  the  individual,  no  analysis  of  the  case  is  possible.  A  third  aberrant 
type,  nigra,  has  given  a  striking  bilateral  gynandromorph  with  gros- 
sulariata (figured  by  Cockayne).  The  genetic  evidence  in  regard  to 
this  type  obtained  by  Punnett  fails  to  show  that  the  character  is  a 
simple  Mendelian  one,  so  that  this  evidence  is  not  available  for  analysis. 

The  most  remarkable  mosaics  of  male  and  female  characters  are 
shown  by  hybrids  of  the  gipsy  moth,  Porthetria  dispar  and  japonica. 
These  mosaics  have  been  described  by  several  observers  (Wiskott. 
1897,  Brake,  1907-1910;  Brake  and  C.Frings,  1911 ;  Goldschmidt;  1912- 
1917;  Poppelbaum,  1914).  We  owe  to  Goldschmidt  not  only  a  most 
complete  account  of  the  hybrids  between  these  two  varieties,  but  of 
hybrids  involving  several  Japanese  local  varieties  of  this  moth.  In  the 
latter  crosses  a  most  astonishing  series  of  mosaics  come  to  light,  not  as 
sporadic  occurrences,  but  as  regular  phenomena  of  the  cross.  In  his 
earlier  work  Goldschmidt  called  these  mosaic  forms  gynandromorphs, 
but  his  later  work  shows,  he  thinks,  that  they  are  different  from 
gynandromorphs;  he  now  calls  them  intersex  forms. 

The  normal  males  and  females  of  the  gipsy  moth  differ  not  only 
in  the  characteristic  sex  differences  of  this  group,  but  in  other  secondary 
sexual  differences  also.  The  Japanese  varieties  show  these  same 
sexual  differences,  though  both  sexes  differ  in  color  and  in  a  few 
minor  points  from  the  European  species.  Japonica  female  by  dispar 
male  gives  equal  numbers  of  daughters  and  sons  that  are  normal  as 
to  sex,  but  the  reciprocal  cross,  dispar  female  by  japonica,  gives 
normal  males  and  intersex  females  in  equal  numbers. 

These  intersexual  females  from  different  crosses  show  a  wide  range 
in  structure,  in  color,  and  in  behavior,  from  almost  normal  females 
at  one  end  of  the  series  to  forms  that  externally  are  about  like  the 
normal  male.  Not  only  are  the  wings  colored  like  those  of  the  normal 
male  (with  occasional  flecks  of  white  like  the  female),  but  the  antennae, 
the  hair,  the  size,  the  genitalia,  and  the  gonads  themselves  are  mosaics 
of  male  and  female  and  intermediate  conditions  also.  These  relations 
are  more  interesting  where  crosses  involving  different  Japanese  races 
are  compared.  ^Vhen  a  race,  Jap.  G  male  is  crossed  to  Jap.  K  female, 
all  Fi  daughters  are  slightly  intersexual.  ^Vhen  a  race,  Jap.  H  female 
is  crossed  to  Jap  G  male,  the  daughters  are  somewhat  more  like  the 
males,  but  the  instincts  are  still  female  and  they  attract  males.  The 
copulatory  organs  are  so  changed  in  the  direction  of  the  male  that 
mating  is  unsuccessful,  and  eggs  can  not  be  laid,  although  the  char- 
acteristic hairy  sponges  are  made.  WTien  a  race,  Eur.  F  female  is 
mated  to  Jap.  G  male,  the  daughters  are  "more  than  half-way 
between  males  and  females."  The  secondary  sexual  characters  are 
almost  male.  The  instincts  and  behavior  are  about  intermediate 
between  those  of  the  two  normal  races.     Males  are  scarcely  attracted 


88  THE    ORIGIN   OF    GYNANDROMORPHS. 

or  not  at  all,  and  no  mating  occurs.  The  copulatory  organs  show  the 
strangest  combinations  of  the  male  and  female  type,  but  there  are 
still  typical  but  rudimentary  ovaries  left.  When  the  race,  Jap.  X 
female  is  crossed  to  Eur.  F  male,  a  still  higher  degree  of  intersexuality 
appears.  Externally  the  daughters  are  "almost  indistinguishable 
from  true  males."  The  instincts  are  entirely  male  and  the  moths 
try  unsuccessfully  to  mate  with  females.  The  gonads  look  like  testes, 
but  in  sections  show  a  mixture  of  ovarian  and  testicular  tissue.  A  step 
further  and  the  daughters  would  be  transferred  into  males. 

The  next  cross  gives  this  final  stage.  When  Jap.  0  male  is  crossed 
to  any  race  of  European  female,  only  males  are  produced,  i.  e.,  all  the 
daughters  become  sons. 

The  reverse  picture  is  given  by  those  combinations  in  which  the 
intersexes  are  sons  partly  changed  over  into  daughters,  a  condition 
that  Goldschmidt  terms  male  intersexuality.  The  wings  are  generally 
streaked  and  in  the  extremest  type  only  a  few  brown  spots  appear  on 
the  wing-veins.  The  testis  may  contain  some  ovarial  tissue,  but  the 
changes  in  the  gonads  do  not  appear  to  run  parallel  to  those  seen  on 
the  surface. 

The  explanation  that  Goldschmidt  offers  for  these  intersexes  is 
entirely  different  from  the  explanation  that  is  demonstrated  for  the 
gynandromorphs  of  Drosophila.  He  accepts  in  part  the  chromosome 
theory  of  sex  determination  and  applies  it  to  the  present  case  on  the 
basis  that  the  female  is  heterozygous  for  the  sex  chromosome  Mm, 
and  the  male  homozygous  MM.  In  addition,  however,  Goldschmidt 
adds  another  set  of  sex-determining  factors  that  he  calls  FF  (inclosing 
them  in  brackets) ,  which  he  locates  in  the  cytoplasm,  that  is,  outside 
the  chromosomal  mechanism.  These  factors  do  not  segregate  (the 
desirability  of  two  F's  is  therefore  not  apparent)  and  are  transmitted 
from  the  female  to  her  sons  and  daughters  alike.  The  FF  factors  stand 
for  femaleness,  which  apparently  includes  the  eggs,  ovaries,  secondary 
sexual  characters,  and  genitalia,  in  fact,  all  parts  associated  with  the 
female.  The  sex  of  a  given  individual  is  dependent  on  the  balance 
struck  by  the  activity  of  the  factors  Mm  and  FF,  one  in  the  chromo- 
somes and  the  other  in  the  cytoplasm. 

The  FF  factors  are  supposed  to  be  located  in  the  cytoplasm  because 
if  a  certain  numerical  value  is  assigned  to  the  egg,  this  value  adheres 
to  the  maternal  line,  no  matter  which  sex  chromosomes  are  introduced 
from  the  male  side  in  successive  generations.  If  the  factors  for  female- 
ness were  carried  by  the  male  and  like  other  paternal  characters  in- 
fluence the  cytoplasm,  their  value  would  be  affected  by  the  kind  of 
males  that  were  employed ;  but  Goldschmidt  has  sho-v^Ti  that  his  results 
work  out  on  the  assumption  that  no  such  effects  need  be  postulated. 

There  is,  however,  another  way  in  which  the  inheritance  of  certain 
factors  along  the  maternal  line  may  be  treated.  Goldschmidt  has 
himself  admitted  this  as  a  possible  interpretation,  although  he  has 


THE   ORIGIN   OF   GYNANDROMORPHS.  89 

adopted  the  cytoplasmic  agency.  In  moths  there  is  present,  in  certain 
species,  a  W  sex-chromosome  analogue  of  the  Y  of  Drosophila  that 
is  always  carried  along  the  female  line.  If  this  chromosome  carries 
factors  it  becomes  one  of  the  conditions  of  the  result  and  the  eggs  will 
always  be  under  its  influence,  and  hence  differ  from  the  spermatozoa 
by  a  constant  difference.  This  assumed  difference  might  account  for 
the  fact  that  in  reciprocal  crosses  the  results  differ  and  certain  phases 
of  the  inheritance  consistently  follow  the  egg.  There  would  be  no 
theoretical  objection  to  calling  this  difference  ''factors  for  femaleness." 
If  crossing-over  took  place  between  the  W  and  the  Z  chromosomes, 
however,  this  constancy  would  disappear.  Until  critical  evidence 
can  be  obtained,  such  as  the  loss  of  the  W  chromosome  from  a  line, 
there  is  no  way  of  proving  or  of  disproving  the  cytoplasmic  versus 
W-inheritance  hypothesis. 

In  regard  to  the  numerical  values  that  Goldschmidt  assigns  to  M 
and  F,  it  is  obvious  that  these  are  from  the  nature  of  the  case  arbitrary, 
such  values  being  assumed  as  will  give  a  consistent  interpretation. 
Whether  this  mode  of  treatment  has  the  advantage  of  a  quantitative 
procedure,  as  claimed,  is  not  so  obvious,  for  the  values  are  simply 
assigned  to  the  data  and  are  not  given  by  any  outside  common  measure, 
such  as  the  chemist  or  physicist  uses  in  quantitative  work.  If,  then, 
the  values  are  only  numerical  assumptions,  the  treatment  is  not,  as 
Goldschmidt  thinks,  lifted  above  the  symbolic  handling  of  the  problem 
of  heredity,  but  stands  on  the  same  footing  as  all  Mendelian  procedure. 
If  the  numerical  values  assumed  give  consistent  results  when  tested 
in  other  crosses  where  other  numerical  values  have  been  assigned,  there 
is  an  undoubted  value  in  handling  the  problem  in  this  way  quite 
irrespective  of  the  question  as  to  what  a  quantitative  treatment  may 
mean. 

As  stated,  Goldschmidt  interprets  his  results  as  depending  on  a 
quantitative  relation  of  the  opposing  factors  for  femaleness  and  for 
maleness.  If  the  quantitative  difTerence  between  the  factors  is  suffi- 
ciently great  in  one  direction  the  individual  is  a  male ;  if  in  the  opposite 
direction  it  is  a  female.  If  the  difference  is  not  sufficiently  great  either 
way  an  intersex  develops.  If  the  quantity  of  the  female  factors  were 
greater  at  the  beginning  a  female  intersex  results ;  if  the  quantity  of  the 
male  factor  were  greater  at  the  beginning  a  male  intersex  develops. 
Both  kinds  of  intersexes  grade  in  different  crosses  all  the  way  from 
nearly  normal  females  to  nearly  normal  males  or  from  nearly  normal 
males  to  nearly  normal  females.  In  each  series  the  sequence  in  which 
the  characters  change  towards  those  of  the  opposite  sex  is  the  reverse 
of  the  order  in  which  they  develop  in  the  individual.  "The  last  organs 
to  differentiate  in  the  pupa  and  the  first  to  be  intersexual  are  the 
branching  of  the  antennae  and  the  coloration  of  the  wings.  The  first 
imaginal  organ  differentiated  in  the  caterpillar  and  the  last  in  the  series 
to  be  changed  toward  the  other  sex  is  the  sex-gland.     And  if  we  apply 


90  THE    ORIGIN    OF    GYNANDROMORPHS. 

this  law  even  to  the  minute  parts  of  a  single  organ,  like  the  copulatory 
organ,  we  find  it  also  to  apply,  as  will  be  demonstrated  later.  Now, 
this  is  the  fact  which,  in  connection  with  the  others,  enables  us  to 
formulate  a  definite  physiological  theory  of  sex-determination."^ 
Goldschmidt  sums  up  the  situation  in  the  following  statement: 

"First,  we  recognized  that  the  different  effects  of  the  same  sex-factors  in 
different  combinations  can  be  understood  only  by  assuming  a  quantitatively 
different  action;  or,  expressed  in  concrete  terms,  that  the  active  substances, 
which  we  represent  as  factors,  are  present  in  different  but  typical  quantities. 
Second,  we  were  obliged  to  assume  that  these  substances  are  distinct  for  each 
sex.  Third,  we  realized  that  in  the  action  of  these  substances  a  time  factor  is 
involved,  which  is  definitely  proportional  to  the  quantities  of  the  factorial 
substances.  From  these  facts  only  one  conclusion  can  at  present  be  drawn: 
that  the  sex-factors  are  enzymes  (or  bodies  with  the  properties  of  enzymes) 
which  accelerate  a  reaction  according  to  their  concentration "^ 

If  the  nature  of  the  character  is  dependent  on  the  relative  quantities 
of  the  male-producing  enzyme  called  andrase  and  of  the  female-pro- 
ducing enzyme  called  gynase,  the  question  arises  how  intersexes  that 
are  mosaics  would  ever  arise,  for  there  is  no  obvious  reason  why  the 
relative  concentration  should  ever  change  in  the  course  of  development 
as  Goldschmidt  must  assume  that  it  does  change.  Still  less  is  it  clear, 
when  the  difference  in  the  concentration  is  less  than  a  given  critical 
difference  (Goldschmidt' s  definite  minimum  value  e),  why  the  enzyme 
that  starts  with  a  lesser  concentration  should  always  overtake  the  other 
quantity,  no  matter  which  one  starts  below.  Until  this  critical  point 
is  explained  all  the  speculation  that  Goldschmidt  brings  to  bear  on  the 
question  only  seems  to  cover  up  the  difficulty  rather  than  to  clear  it  up. 
Goldschmidt  appears  to  have  overlooked  this  difficulty  and  sets  up  the 
opposite  one,  viz,  that  it  is  difficult  to  see  why  every  gipsy  moth  is  not 
an  intersex.  He  meets  this  supposed  difficulty  by  the  consideration 
of  the  rate  of  development  of  the  insect.  Whether  his  answer  to  this 
difficulty  is  valid  or  not,  it  does  not  seem  to  meet  the  difficulty  which 
to  us  seems  the  real  one. 

Even  were  it  established  that  many  of  the  changes  in  embryonic 
and  larval  development  are  due  to  enzymes — a  point  that  we  are  far 
from  wishing  to  dispute — it  need  not  follow  that  the  segregating  genes 
that  give  rise  to  them  are  also  these  same  enzymes.  To  treat  these 
half-way  stages  as  the  genes  themselves  is  at  present  not  without 
danger,  because  even  if  the  genes  are  enzymes  it  by  no  means  follows 
that  the  quantity  of  the  gene  is  to  be  measured  by  the  product  of  the 
enzyme  arising  from  it. 

In  his  latest  communication  Goldschmidt  states  his  belief  that  the 
sex-factors  in  the  different  races  of  gipsy  moths  are  multiple  allelo- 
morphs and  compares  them  to  the  series  of  factors  that  Castle  has 

1  Goldschmidt.     A  Further  Contribution  to  the  Theory  of  Sex.     {Journ.  Exp.  ZooL,  vol.  22, 
No.  3,  April  1917,  p.  597). 

2  Ibid,  p.  598. 


THE    ORIGIN    OF   GYNANDROMORPHS.  91 

found  in  his  series  of  hooded  rats.  So  far  as  we  know,  the  conclusion 
that  Castle's  series  of  characters  are  mainly  due  to  multiple  allelo- 
morphs is  far  from  being  established;  on  the  contrary,  we  are  inclined 
to  think  that  his  evidence  indicates  that  he  is  dealing  mainl}''  with  a 
case  of  multiple  factors.  Some  of  the  evidence  that  Goldschmidt 
himself  furnishes  for  the  gipsy  moths  is  perhaps  also  capable  of  inter- 
pretation in  the  same  way. 

Goldschmidt  has  shown  in  some  detail  that  the  characters  or  organs 
of  the  intersexes,  such  as  the  wings  or  external  genitalia,  are  mosaics — 
i.  e.,  relatively  large  segments  or  pieces  are  entirely  male  or  female. 
In  the  case  of  the  wings  there  is  no  obvious  regularity  in  the  mosaic 
pattern,  for  the  right  hind  wing  may  be  entirely  different  from  the 
left  hind  wing,  and  the  male  parts  of  the  right  wing  do  not  by  any 
means  correspond  to  the  male  parts  of  the  left  wing,  nor  does  either 
conform  strictly  to  any  underlying  structure,  such  as  the  veins.  In 
so  far,  then,  as  each  part  is  strictly  male  or  female  and  not  a  blend  of 
both,  the  gipsy-moth  intersex  is  like  the  Drosophila  gynandromorph. 
The  results  are,  however,  unlike  the  Drosophila  gynandromorphs  in 
that  in  the  gipsy-moth  hybrids  the  phenomenon  must  occur  very 
frequently.  Baltzer  has  shown  for  certain  sea-urchin  hybrids  that 
when  the  cross  is  made  one  way  there  is  always  an  irregular  (?)  elimina- 
tion of  chromosomes,  and  this  result  invites  at  least  a  comparison  with 
the  gipsy  hybrids.  A  solution  of  the  case  of  intersexes  in  the  gipsy 
moth  could  probably  be  reached  by  the  discovery  and  study  of  sex- 
linked  characters. 

Several  gynandromorphs  of  Colias  have  been  described  (see  Cock- 
ayne), but  of  unknown  parentage.  In  the  moth  Algia  tau  also  several 
gynandromorphs  have  been  recorded,  but  the  published  evidence 
known  to  us  does  not  give  any  clue  as  to  their  origin. 

As  has  been  stated,  the  great  majority  of  gynandromorph  Lepidop- 
tera  are  not  hybrids,  but  show  the  secondary  sexual  characters  of  the 
male  on  one  side  and  the  secondary  sexual  characters  of  the  female 
on  the  other.  There  are,  however,  a  few  gj^nandromorphs  in  this 
■  group  that  show  racial  or  specific  differences  along  with  the  male  and 
female  characters.  Amongst  these  only  a  few  have  a  known  ancestry, 
and  amongst  these  again  it  is  seldom  known  whether  the  characters 
exhibited  are  sex-linked  or  not.  Even  if  they  are  sex-linked  the 
evidence  fails  to  discriminate  between  a  result  that  depends  only  on 
sex-chromosomal  differences  and  a  result  that  depends  on  a  full  chro- 
mosome group.  A  search  through  most  of  the  available  literature  has 
brought  to  light  only  a  few  cases  that  bear  on  the  theories  that  have 
been  already  discussed.  Nevertheless,  it  is  probable  that  a  more 
thorough  search  through  the  voluminous  literature  might  furnish  more 
of  the  critical  evidence  desired.  It  is  not  improbable  that  entomolo- 
gists who  have  made  varietal  crosses  may  be  able  to  supply  some  of  the 
needed  data. 


92  THE    ORIGIN   OF   GYNANDROMORPHS. 

From  the  elaborate  list  of  gynandromorphs  published  in  1896  and 
1897  by  Schultz,  and  from  the  admirable  resume  by  Cockayne  in  1915, 
the  following  cases  have  been  chosen  as  the  most  instructive  ones  on 
record. 

Wheeler  (1915)  describes  a  gynandromorph  from  a  cross  of  Smerin- 
thus  ocellatus  by  Amorpha  populi  {hyhridus).  The  right  side  is  female, 
the  left  side  male. 

"The  left  wings  are  pinkish,  as  in  ocellatus,  while  the  right  wings  are  entirely 
gray.  The  eye-spots  of  ocellatus  are  well  developed  on  both  wings,  as  is 
also  the  red  basal  patch  of  populi.  Right  antennae  like  female  populi,  left 
like  male  ocellatus.     Right  half  of  body  light  gray,  left  half  brownish  gray.' ' 

Since  both  sides  of  the  body  show  some  characters  that  belong 
to  both  parents,  it  is  highly  probable  that  parts  of  both  parental  nuclei 
are  present  on  both  sides  of  the  gynandromorph. 

Briggs  (1881)  has  also  described  a  hybrid  gynandromorph  showing 
the  characters  of  Smerinthus  ocellatus  and  populi — right  side  ocellatus, 
'  left  side  populi.  A  figure  is  given,  but  no  description.  Whether  from 
the  figure  it  would  be  possible  to  determine  whether  some  characters  of 
both  parents  are  present  on  both  sides  might  no  doubt  be  determined 
by  an  expert,  but  the  all  too  brief  text  gives  no  information. 

Harrison  crossed  Ennomos  suhregnaria  male  by  E.  quercinaria 
female,  and  obtained  many  hybrids  that  were  "practically  the  mean  of 
the  parents,  except  that  they  leaned  in  the  color,  both  of  the  head  and 
body  and  possibly  in  the  general  structure  of  the  warts  and  tubercles, 
to  the  male  parent."     In  describing  one  of  these,  Harrison  says: 

"At  first  sight  it  is  merely  a  male  specimen  with  the  left  anterior  female. 
Dissection  and  close  examination  betray  much  more  interesting  characters 
than  that.  The  genitalia  (fig.  4),  although  nearly  so,  are  not  quite  purely 
male ;  the  right  lobe  of  the  uncus  is  replaced  by  a  fully  developed  right  ovi- 
positor or  lobe,  wliile  the  gathous  on  the  same  side  is  greatly  disturbed,  and 
acts  as  if  it  were  homologous  to  the  female  directing  rods.  In  addition, 
whilst  the  coloration  of  both  sides  of  the  body  is  male,  the  shape  of  the  right 
wing  is  female." 

Harrison  points  out  that  "whilst  the  majority  of  the  characters  of 
the  right  side  were  female  the  color  was  wholly  male."  It  appears 
from  this  description  that  hybrid  characteristics  appeared  throughout, 
which  indicates  that  other  chromosomes  than  the  sex  chromosome 
were  involved  on  both  sides;  but  since  so  small  apart  was  distinctly 
female,  it  is  not  entirely  clear  that  the  hybrid  coloration  affected  this 
part  too.  He  states  (as  above)  that  "while  the  majority  of  characters 
of  the  right  side  were  female  the  color  was  wholly  male.' '  Apparently 
by  male  he  means  hybrid  male  coloration,  and  if  so  the  case  is 
instructive. 

Harrison  obtained  another  aberrant  individual  from  this  cross.  He 
states  that  "the  right  being  exactly  that  of  a  normal  hybrid,  whilst 


THE    ORIGIN   OF   GYNANDROMORPHS.  93 

the  left  side  is  pure  subregnaria."  The  text  leaves  it  uncertain 
whether  the  individual  is  a  gynandromorph,  although  this  appears 
not  to  be  the  case,  for  while  the  former  specimen  is  classified  as  a 
gynandromorph,  this  one  is  put  into  a  separate  paragraph  entitled 
"Asymmetrical  specimen."  Its  genitalia  are  said  to  "present  the 
same  division  of  characters  as  those  exhibited  externally,  as  may  be 
seen  from  figure  8,  which  shows  the  furca  and  the  penis,  the  left  side  being 
that  of  the  hybrid,  whilst  the  right  is  evidently  subregnaria,  conforming 
itself  to  the  structure  of  the  left." 

Harrison  explains  the  result  as  due  to  two  spermatozoa  entering 
the  egg,  the  nucleus  of  one  of  which  conjugated  as  usual  with  the  egg- 
nucleus,  but  the  nucleus  of  the  other,  instead  of  degenerating,  gave 
rise  to  the  nuclei  determining  the  right  side  of  the  body,  which  would 
then  be  pure  subregnaria  and  differs  from  the  hybrid  left  side,  which 
resulted  from  the  conjugation  of  nuclei  derived  from  two  different 
species.  Insofar  as  one  side  is  purely  paternal,  this  case  is  in  line  with 
Morgan's  hypothesis  of  multiple  fertilization  and  does  not  conform 
to  Boveri's  view.  On  the  other  hand,  there  is  the  same  cytological 
difficulty  here  as  encountered  in  Toyama's  case,  namely,  that  in  Lepi- 
doptera  the  male  is  the  homozygous  individual.  A  single  nucleus 
should  give  rise,  therefore,  to  a  female,  but  here  probably  both  sides, 
and  certainly  the  pure  subregnaria,  side  is  male. 

The  hypothesis  of  elimination  will  not  help  out  here,  for  even  if  a 
quercinaria  daughter  chromosome  was  the  one  lost,  the  single  sex 
chromosome  should  give  rise  to  female  parts.  On  the  other  hand, 
one  of  the  alternative  views  suggested  above  for  Abraxas  covers  this 
case,  viz,  the  view  that  an  egg  had  two  nuclei  or  that  several  sperma- 
tozoa entering  and  fusing  in  pairs  gave  rise  to  the  male  parts. 

Cockayne  (1916)  described  a  hybrid  gynandromorph  that  came 
from  a  cross  of  Amorpha  ocellatus  male  by  A.  populi  female.  It  was 
male  on  the  right  side  and  female  on  the  left.  Although  the  wings 
did  not  expand,  it  was  evident  that  on  both  sides  the  specific  characters 
were  intermediate  between  the  two  parents.  The  insect  had  neither 
ovary  nor  testis,  but  the  external  genitalia  were  male  on  one  side  and 
female  on  the  other. 

Vasseler  described  a  bilateral  gynandromorph  of  Argynnis  paphia 
in  which  the  left  side  was  male  and  paphia,  and  the  right  side  was  female 
and  valesina.  The  latter  is  a  characteristic  varietal  form.  The  result 
can  be  explained  by  dislocation  of  the  sex  chromosome  on  the  basis 
that  the  factor  of  valesina  is  sex-linked  and  that  it  is  recessive. 

According  to  Rudolphi,^  a  gynandromorph  was  sent  to  McLeay  from 
Rio  de  Janeiro,  var.  Papilio  laodicus  on  the  female  side  and  P.  polycaon 
on  the  male  side.     Dr.  F.  E.  Lutz  has  been  good  enough  to  look  up 

'  Rudolphi,  D.  K.  A.,  Abh.  phys.   klass.   Konig,  Akad.  wiss.,  Berlin,  1825.     See  Trans.  Linn. 
Soc,  XIV,  p.  584. 


94  THE    ORIGIN   OF   GYNANDROMORPHS. 

for  me  the  history  of  the  "species"  question.     The  following  note  I 
owe  to  him: 

"Papilio  androgens  is  quite  variable  and,  furthermore,  shows  sexual  di- 
chromatism.  Three  varieties  are  accepted:  typical  androgens  (Colombia 
to  Trinidad,  Guianas,  Amazon,  southward  to  Bolivia  and  western  Matto 
Grosso),  epidarniis  (Mexico  to  Panama,  Cuba,  Haiti,  and  Saint  Lucia),  and 
laodocus  (Brazil  and  Paraguay).  The  name  polycaon  has  been  used  by 
authors  for  each  of  these  forms  and  has  been  applied  to  both  males  and 
females.  The  name  laodicns  has  usually  (always?)  been  applied  to  the  female. 
It  seems  probable  that  the  specimen  in  question  was  an  ordinary  gynandro- 
morph  of  Papilio  androgens  laodicus." 

Cockayne  has  discussed  at  length  the  evidence  showing  that  gynan- 
dromorphism  is  commoner  in  certain  species  than  in  others,  and 
reached  the  conclusion  that  this  is  not  due,  in  several  cases  at  least, 
to  the  more  striking  characters  involved,  but  rather  to  some  peculiar 
defect  in  the  sex-determining  machinery  of  these  species.  Moreover, 
there  appears  to  be  good  evidence  favoring  the  view  that  in  certain 
families  the  number  of  gynandromorphs  is  greater  than  in  the  race  as 
a  whole.  The  cause  of  this  "inheritance"  is  obscure.  Possibly  these 
are  cases  of  intersexuality  rather  than  of  true  gynandromorphism. 

The  evidence  is  more  certain  that  gynandromorphs  are  more  com- 
mon in  certain  hybrid  combinations  than  in  the  pure  parent  species 
involved  in  the  cross.  Whether  such  combinations  are  generally  due 
to  the  greater  liklihood  of  chromosomal  elimination — a  view  that  would 
seem  a  priori  possible — or  to  "partial  fertilization"  or  to  polyspermy 
can  only  be  determined  when  more  definite  material  is  obtained  that 
furnishes  opportunity  for  genetic  evidence. 

GYNANDROMORPHS  IN  OTHER  INSECTS. 

The  scarcity  of  gynandromorphs  in  other  groups  of  insects  is  prob- 
ably due  in  part  to  the  absence  of  conspicuous  differences  between  the 
male  and  female  in  such  groups  as  beetles  or  to  certain  groups  being 
less  collected  or  observed  than  others.  We  have  made  no  attempt 
to  search  out  in  the  literature  all  references  to  gynandromorphs. 
Occasional  references  to  gynandromorphs  in  earwigs,  Orthoptera, 
beetles,  and  bugs  are  to  be  found  in  the  International  Catalogue. 

GYNANDROMORPHS  IN  SPIDERS. 

In  a  recent  paper  J.  E.  Hull  has  brought  together  the  few  cases  of 
gynandromorphs  in  spiders  that  are  known.  The  best  example  is 
that  described  by  Kulezynski  that  is  male  on  one  side  and  female  on 
the  other.  Another  described  by  Falconer  was  also  male  on  one  side, 
female  on  the  other.  Another  gynandromorph  described  by  the  author 
(Hull)  is  male  and  female  anteriorly  and  female  and  male  posteriorly 
(quadripartite).     Three  other  cases  of  bilateral  gynandromorphs  have 


THE    ORIGIN   OF   GYNANDROMORPHS.  95 

been  reported,  according  to  Hull,  and  one  or  two  other  gynandromorphs 
incompletely  described. 

Most  of  the  gynandromorphs  in  spiders  belong  to  one  family.  Thus 
amongst  the  232  species  of  British  Linyphiida?  there  are  seven  gynan- 
dromorphs known,  while  amongst  the  377  other  species  only  one. 
Hull  estimates  that  gynandromorphs  are  nine  times  as  frequent  in 
the  Linyphiidae  as  in  all  the  rest  taken  together. 

Since  the  male  is  heterozygous  for  the  X  chromosome  in  spiders  the 
results  may  have  the  same  explanation  as  in  insects,  but  since  no 
hybrid-gynandromorphs  have  been  found  it  is  impossible  to  do  more 
than  point  out  a  possible  solution. 

GYNANDROMORPHS  IN  CRUSTACEA. 

The  frequency  of  bilateral  gynandromorphs  in  insects  is  in  marked 
contrast  to  the  almost  total  absence  of  such  types  in  the  large  group 
of  Crustacea.  It  is  true  that  in  the  latter  there  are  examples  of  inter- 
sexual  individuals,  but  it  is  not  clear  whether  these  come  under  the 
same  category  as  the  gynandromorph  insects  or  are  special  cases  more 
like  hermaphrodites. 

It  may  be  of  interest  to  observe  in  this  connection  that  in  the 
Crustacea  no  sex  chromosomes  have  as  yet  been  discovered,  but  it 
may  be  replied  that  this  may  be  due  to  the  well-known  difficulties  of 
technique  rather  than  to  a  real  difference.  However  this  may  be, 
there  are  certain  well-ascertained  facts  about  some  of  the  Crustacea 
suggesting  that  the  condition  of  hermaphroditism  is,  so  to  speak,  nearer 
the  surface  in  the  sense  that  the  swing  towards  one  sex  or  the  other  in 
a  given  individual  is  brought  about  more  readily  by  age  or  environ- 
mental conditions  than  in  other  groups  where  a  change  is  more  difficult 
because  the  internal  hereditary  factor  differences  prevail  over  ordinary 
external  or  age  differences.  For  example,  in  the  group  of  cirripeds 
hermaphroditic  species  and  species  with  separate  sexes  exist,  as  well 
as  species  related  to  hermaphroditic  species  in  which  the  females  have 
complemental  males.  It  has  been  suggested  that  these  males  are 
themselves  only  those  arrested  females  or  hermaphrodites  that  settle 
down  and  become  parasitic  on  the  larger  sessile  females ;  in  other  words, 
that  these  males  had  the  potentiality  of  becoming  females  if  they  had 
chanced  to  lead  a  different  existence.  There  are  families  amongst 
the  isopods  that  are  hermaphroditic.  Certain  species  of  amphipods 
are  said  to  be  males  when  young,  females  when  older.  Eggs  have 
been  found  at  certain  stages  intermediate  in  size  between  the  small 
male-producing  eggs  and  larger  female-producing  eggs. 

The  transformation  of  some  of  the  secondary  sexual  characters  of 
the  male  into  those  of  the  female  in  certain  parasitized  crabs  has  a 
bearing  both  on  the  relation  of  these  characters  to  the  sex-glands  and 
possibly  also  on  the  causes  that  determine  sex  in  the  Crustacea. 


96  THE    ORIGIN   OF   GYNANDROMORPHS. 

Giard,  and  later  Geoffrey  Smith,  have  described  the  changes  that 
take  place  when  crabs  are  parasitized  by  Sacculina  and  other  para- 
sitic Crustacea.  When  the  male  spider-crab  Inachus  dorsettensis  is 
parasitized  by  Sacculina  the  abdomen  becomes  wide  like  that  of  the 
female,  and  its  posterior  appendages,  that  are  absent  in  the  male, 
develop  and  become  somewhat  like  those  of  the  female.  The  chelse 
likewise  come  to  resemble  those  of  the  female.  The  testis,  which 
may  not  be  affected  at  first,  may  later  degenerate  to  some  extent,  and 
in  one  case  after  the  parasite  had  fallen  off  the  regenerating  testis 
produced  eggs.  It  was  formerly  supposed  that  the  degeneration  of 
the  testis  might  be  the  cause  of  the  change  in  the  secondary  sexual 
organs,  although  no  such  relation  between  gonad  and  soma  is  known 
to  exist  in  this  group;  but  the  work  of  Geoffrey  Smith  seemed  to  him 
to  suggest  that  the  results  are  directly  caused  by  the  parasite  itself 
by  stimulating  the  formation  of  fatty  substance  whose  presence  in  the 
blood  may  cause  eggs  to  develop  and  the  secondary  sexual  organs  of 
the  female  to  appear.  In  other  words,  'Hhe  crab  comes  to  resemble 
a  female  because  the  physiology  of  its  body-tissues  has  been  changed 
from  the  male  to  the  female  type"  (Doncaster).  Whatever  the 
explanation  may  ultimately  be  found  to  be,  the  fact  of  the  change  is 
important.  The  result  falls  into  line  with  the  other  evidence  con- 
cerning sex  determination  in  the  Crustacea,  viz,  that  maleness  and 
femaleness  are  not  so  fixed  by  internal  genetic  factors  if  such  exist, 
but  that  the  balance  may  be  shifted  by  other  agents  as  well.  A  parallel 
case  is  known  in  the  Andrenine  bees,  parasitized  by  another  insect, 
Stylops.  According  to  Perez,  the  stylopized  males  come  to  resemble 
in  certain  respects  the  females,  and  inversely  the  stylopized  females  the 
males.  '  The  sex-glands  are  not  always  affected.  If  in  bees  as  in 
moths  the  secondary  sexual  characters  are  independent  of  the  gonads, 
the  effect  of  Stylops  must  be  either  directly  on  the  host  or  through  a 
change  in  its  metabolism.  W.  M.  Wheeler  has  described  stylopized 
American  wasps  of  the  genus  Polistes.  No  change  in  the  secondary 
characters  takes  place,  at  least  not  to  any  marked  extent. 

The  decapods  have,  as  a  rule,  males  and  females  sharply  dis- 
tinguished, although  the  females  of  Gehia  major  have  only  ovaries,  the 
males  have,  behind  the  testes,  ovaries  more  or  less  developed.  A 
crab,  Lysmata  seticaudata,  has  as  a  rule  both  ovaries  and  testes,  with 
their  ducts.  Several  hermaphroditic  crayfish  have  been  described, 
especially  by  Faxon  (1898)  and  Hay  (1907).  One  (text-figure  69)  had 
ovaries  on  both  sides,  also  on  the  right  side  a  testis  (without  sperm) 
and  a  vas  deferens.  It  had  the  external  characters  of  a  "first  form" 
male  except  for  the  openings  of  the  oviducts  on  the  third  pair  of  legs. 
It  appears,  at  least  in  the  genus  Cambarus,  that  hermaphroditic  indi- 
viduals are  females  which,  "owing  to  some  ambiguity  of  the  formative 
cells  in  the  embryo,  have  developed  to  a  greater  or  less  degree  the 


THE    ORIGIN    OF   GYNANDROMORPHS.  97 


characters  of  the  opposite  sex.     The  condition  is  a  very  rare  one  and 
is  usually  shown  in  the  external  organs  only." 

In  the  Philosophical  Transactions  for  1734  is  a  full  account  of  a 
bilateral  gynandromorph  lobster  by  Dr.  F.  Nichols.  The  drawings 
of  the  external  parts  show  that  the  animal  is  female  on  the  right  side 
and  male  on  the  left.  Dissection  showed  an  ovary  with  eggs  on  the 
right  side,  and  a  testis  with  vas  deferens  on  the  left.  This  case  is 
exactly  like  the  bilateral  gj^nandromorphs  of  Drosophila,  and  is  the 
only  case  known  to  us  of  a  strictly  bilateral  type  of  gynandromorph 
in  the  group  Crustacea. 

Olga  Kuttner  (1909)  found  a  wild  individual  of  Daphnia  pulex  that 
had  some  male  characters  on  one  side  but  had  two  ovaries.  Twelve 
broods  were  produced  and  in  nearly  every  brood  some  individuals  were 
mixed  gynandromorphs,  but  nearly  all  were  predominantly  female. 

A  similar  case  has  been  recorded  by  Banta  for  Simocephalus  vetulus, 
(1916).  In  a  pedigreed  strain  there  ''suddenly 
appeared"  a  large  number  of  "sex  intergrades — 
males  ^vith  one  or  more  female  secondary  sex 
characters,  females  with  one  to  several  male 
characters,  and  some  hermaphrodites  with  vari- 
ous combinations  of  male  and  female  secondary 
sex  characters."  The  more  extreme  intersex 
individuals  fail  to  propagate;  others,  less  modi- 
fied, reproduce.  By  propagating  from  female  \jX^\l-^!^J:"'^^^^'d  r 
intergrades  mixed  broods  of  males,  females,  and 
intergrades  are  obtained.  The  noteworthy 
point  here  is  that  the  intergrades  are  mosaics 
rather  than  blended  forms  of  the  two  sexes.  text-figuhe  69. 

GYNANDROMORPHS  IN  MOLLUSCS. 

The  molluscs,  like  the  Crustacea,  contain  a  number  of  hermaphro- 
ditic species,  but  there  are  also  species  with  separate  sexes.  Here, 
too,  cytological  study  has  failed  as  yet  to  demonstrate  sex  chromo- 
somes. One  species  of  Crepidula  is  male  in  the  juvenile  state  and 
female  in  older  individuals,  at  least  when  certain  external  conditions 
are  fulfilled.  Gould  has  recently  shown  that  when  young  males  are 
placed  in  the  vicinity  of  large  females  the  males  absorb  their  testes 
and  genitalia  (ducts  and  penis)  and  develop  ovaries  and  oviducts. 
This  case  recalls  in  many  ways  the  conditions  in  Bonellia  as  described 
by  Baltzer.  If  the  embryos  of  Bonellia  are  isolated  they  become  sexual 
females  without  showing  the  male  stage.  If,  however,  the  embryo, 
when  ready  to  settle  down,  comes  to  rest  on  the  proboscis  of  a  female 
it  develops  into  a  rudimentary  male.  A  few  embryos  in  cultures  may 
show  intermediate  or  rather  hermaphroditic  conditions.  The  cirri- 
peds  referred  to  above  appear,  according  to  one  interpretation,  suscep- 


98  THE    ORIGIN    OF    GYNANDROMORPHS. 

tible  of  similar  modifications,  according  to  whether  they  remain  free  or 
become  parasitic  on  a  female. 

The  conditions  in  Crustacea  and  molluscs  seem  to  show  that,  in 
some  cases  at  least,  the  animals  are  essentially  hermaphrodites  and 
that  external  conditions  and  age  are  important  factors  in  determining 
the  sex  of  the  individual.  These  cases  recall  the  phenomena  shown  by 
many  flowering  plants  where  at  one  stage  or  under  certain  conditions 
the  male  organs  develop,  under  other  conditions  the  female  organs. 
If  in  such  cases  sex-determining  genes  are  present,  their  influence  may 
be  readily  overcome  by  external  agencies  or  by  age  itself,  which  is  in  a 
sense  a  condition  in  which  some  part  of  the  body  (through  its  output) 
acts  as  an  external  agent  to  other  parts. 

GYNANDROMORPHS  IN  ECHINODERMS. 

Cuenot  (1898)  and  Delage  (1902)  described  each  a  mature  starfish 
(Asterias  glacialis)  that  had  small  patches  of  testis  (with  sperm)  in 
the  ovary,  and  Buchner  (1911)  has  recorded  a  similar  case.  Herlandt 
has  recently  described  a  sea-urchin  (Paracentrotus)  that  had  three 
normal  and  one  "dark"  testes  and  a  large  ovotestis  with  functional 
ova  and  sperm.  Artificial  fertilization  with  the  products  of  this  ovo- 
testis was  successful,  and  the  larvae  were  normal.  Since  Tennant  has 
shown  for  the  sea-urchin  that  the  female  is  homozygous  and  the  male 
heterozygous  for  the  X  chromosome,  these  cases  can  be  easily  explained 
on  the  hypothesis  of  elimination  of  an  X  chromosome — the  resulting 
parts  being  male. 

GYNANDROMORPHS  IN  VERTEBRATES. 

The  group  of  vertebrates  shows  as  a  rule  sharp  separation  into  two 
sexes,  but  the  evidence  relating  to  the  factors  involved  is  often  so 
little  known  that  the  group  as  a  whole  is  difficult  to  handle.  In  one 
subdivision,  the  birds,  the  female  is  the  heterogametic  sex  with  regard 
to  sex  chromosomes,  while  in  mammals,  certainly  in  man,  it  is  the  male 
that  is  heterogametic.  The  contrast  here  is  the  same  as  that  in  insects, 
where  the  moths  resemble  the  birds  and  the  flies  man.  In  some  of 
the  lower  groups  there  are  evidences  of  hermaphroditism  or  of  transi- 
tory sex  conditions.  It  becomes  necessary,  therefore,  to  take  up  the 
different  groups  independently. 

GYNANDROMORPHS  IN  FISHES. 

Myxine,  according  to  Cunningham  and  Nansen,  is  male  when  young 
and  later  becomes  female.  In  the  young  the  anterior  portion  of  the 
testis  is  male,  the  posterior  female;  the  testicular  part  atrophies  after 
it  has  functioned  as  a  testis.  But  the  later  results  of  the  Schreiners 
indicate  that  while  young  Myxine  is  a  true  hermaphrodite  as  far  as 
the  histological  structure  of  the  glands  is  concerned,  it  is  not  so  func- 


THE    ORIGIN   OF   GYNANDROMORPHS.  99 

tionally.  They  believe  that  any  one  individual  after  passing  through 
this  stage  becomes  definitely  either  male  or  female,  although  certain 
individuals  remain  sterile,  neither  alternative  being  realized  (quoted 
from  Caullery,  Les  Problemes  de  la  Sexuality,  1913,  p.  53.) 

A  gynandromorph  was  described  in  1914  by  Vayssiere  and  Quintaret 
in  one  of  the  sharks,  Scyllium  stellare.  The  left  pelvic  fin  was  female, 
the  right  male  with  a  well-developed  clasper.  An  ovary  and  both  ovi- 
ducts were  present.  On  the  right  side  there  was  a  testis,  with  normal 
male  ducts  on  this  side  only. 

Miss  Ruth  C.  Bamber  described  (1918)  a  hermaphroditic  shark, 
Scythum  cavicula,  in  which  both  testes  were  present.  The  anterior 
end  of  the  right  testis  had  ovarian  tissue.  Normal  oviducts  were 
present  and  the  male  ducts  were  well  developed.  Externally  this 
animal  was  typically  a  male  with  well-developed  claspers. 

Most  of  the  bony  fishes  have  separate  sexes,  but  certain  species 
(Serranus)  are  true  hermaphrodites.  (See  Shattuck  and  Seligmann.) 
Other  species  give  exceptional  individuals  that  have  traces  of  both 
sexes.  Chidester  has  described  a  male  fundulus  with  ova  attached 
to  the  mesentery  of  the  intestine  and  liver. 

GYNANDROMORPHS  IN  AMPHIBIA. 

The  sharp  separation  into  adult  males  and  females  is  characteristic 
of  the  group  Amphibia.  According  to  Miss  Stevens  there  is  a  pair 
of  XY  chromosomes  in  the  male  of  one  of  the  urodeles,  but  in  a  frog, 
Rana  pipiens,  Swingle  states  there  is  only  one  sex  chromosome  in 
the  male.  Certain  species  of  frogs  pass  through  a  stage  that  appears 
to  be  hermaphroditic — at  least  individuals  that  later  become  males 
may  contain  in  the  young  tadpole  stage  large  cells  that  appear  to  be 
incipient  ova,  which  later  disappear  when  the  spermatozoa  are  formed. 
In  the  adult  toad  there  is  a  region  anterior  to  the  testis  proper  called 
Bidder's  organ,  in  which  ova-like  cells  are  present.  There  are  a 
number  of  observations  in  the  older  Uterature  to  the  effect  that  well- 
fed  tadpoles  produce  more  females  than  males,  and  lice  versa,  that 
starved  tadpoles  give  an  excess  of  males.  On  the  other  hand,  there 
are  other  later  observations  that  flatly  contradict  these  conclusions. 
There  are  some  observations,  especially  those  of  King,  that  show  the 
proportion  of  males  and  of  females  may  be  determined  by  treating  the 
eggs  (or  even  the  sperm)  with  certain  substances  in  solution,  but 
whether  the  change  is  due  to  the  chemicals  injuring  one  kind  of  sperm 
(or  of  egg)  more  than  the  other  kind,  or  whether  the  change  is  of  a 
kind  to  really  determine  the  sex,  irrespective  of  the  combinations 
formed  by  the  germ-cells,  is  open  to  debate.  The  most  remarkable 
observations  on  Amphibia  are  those  of  Richard  Hertwig  and  his  pupils, 
particularly  Kuschakowitsch.  They  show  that  by  delaying  the 
fertilization  of  the  egg  there  is  caused  an  increase  in  the  number  of 


100  THE   ORIGIN    OF   GYNANDROMORPHS. 

males  produced.  By  prolonging  the  time  to  the  point  where  the  eggs 
are  almost  ready  to  die,  all  or  almost  all  of  the  frogs  become  males. 
The  result,  moreover,  appears  from  Kuschakowitsch's  results  not  to 
be  due  to  selective  mortality.  Hertwig  attempts  to  explain  the  results 
in  accordance  with  his  view  of  nuclear  size  versus  cell  size,  but  the 
case  seems  peculiarly  ill  suited  to  this  interpretation,  because  the 
nucleus  has  dissolved  and  the  chromosomes  are  already  in  the  meta- 
phase  condition  when  the  eggs  enter  the  oviduct,  and  it  is  here  that 
the  delay  occurs.  It  is  not  at  all  obvious  how  delay  in  this  condition 
can  have  much  to  do  with  cell  size  versus  nuclear  size.  One  of  us 
(Morgan,  1913)  has  suggested  that  Hertwig's  results  may  be  due  to 
a  sort  of  parthenogenetic  development  in  those  eggs  whose  progress 
is  held  back.  Such  a  result  might  be  due  either  to  the  egg  nucleus 
giving  rise  to  the  embryo  (the  sperm  merely  starting  it,  but  taking  no 
further  part  in  the  development),  or  to  the  sperm  nucleus  becom- 
ing the  functional  one,  the  egg  nucleus  having  disintegrated  in  the 
interval.  In  support  of  such  a  view  may  be  cited  the  observation 
of  Oscar  Hertwig  and  of  Gunther  and  Paula  Hertwig  on  frogs'  eggs 
treated  with  radium.  They  interpret  certain  of  their  results  as  due 
to  mononuclear  development  of  the  treated  egg  or  sperm.  The  sex 
of  the  resulting  larvae  was  not  determined.  The  recent  results  of 
Loeb  and  Bancroft  and  of  Loeb  have  shown  that  frogs'  eggs,  in- 
cited to  development  by  Bataillon's  puncture  method,  give  rise  to 
males  and  females  in  a  few  cases  in  which  the  frog  stage  was  reached. 
Loeb  states  (1918)  that  the  parthenogenetic  males  have  the  double 
number  of  chromosomes.  Herlandt  describes  the  parthenogenetic 
embryos  of  the  frog  as  arising  in  such  a  way  that  the  haploid  number 
of  chromosomes  at  the  first  division  must  be  supposed  to  be  present, 
but  Brachet  states  that  he  has  found  the  diploid  number  of  chromo- 
somes present.  Until  further  cytological  work  is  done  the  explanation 
of  the  facts  remains  obscure. 

Swingle  has  recently  described  hermaphroditic  stages  of  the  young 
frog  Rana  pipiens.  Both  eggs  and  sperm  are  formed  in  the  gonad  of 
some  individuals,  whereas  other  individuals  have  only  testes  or  ovaries, 
i.  €.,  not  mixed.  He  suggests  the  possibility  that  an  irregular  distri- 
bution of  the  sex  chromosomes  in  early  oogonial  divisions  may  account 
for  this  condition.  In  one  hermaphroditic  individual  he  found  13  chro- 
mosomes in  the  spermatocytes,  one  of  which  is  dumbbell-shaped,  and 
this  he  thinks  is  the  sex  chromosome.  In  most  first  spermatocyte 
divisions  the  12  autosomes  divide,  but  the  dumbbell-shaped  chromo- 
some goes  to  one  pole.  Exceptionally,  however,  the  chromosome 
divides,  one  half  going  to  each  pole.  An  irregular  division  of  the  kind 
(or  of  some  other  kind),  if  it  occurred  at  an  earlier  stage,  might  give 
the  chromosomal  combination  that  would  produce  an  egg,  even  in  a 
potential  male. 


THE    ORIGIN   OF   GYNANDROMORPHS.  101 

Among  the  urodeles,  la  Valette  St.  George  has  described  a  newt 
having  external  male  characters  and  an  ovotestis  on  each  side.  Among 
the  Anura  several  cases  of  hermaphroditism  beside  those  referred  to 
above  have  been  described.  Loisel  described  a  frog  with  the  secondary 
sexual  characters  of  the  male.  On  the  right  side  no  gonad  was  present 
and  on  the  left  the  ovary  was  small  and  pigmented.  It  had  no  ova. 
This  condition  suggests  that  the  male  character  had  developed  as  a 
result  of  natural  castration,  but  on  the  other  hand,  the  two  conditions 
may  have  had  some  common  cause.  Other  cases  of  hermaphroditism 
in  frogs  and  toads  are  reported  by  Spengel,  Knappe,  Hoffman,  and 
Stephan. 

GYNANDROMORPHS  IN  REPTILES. 

Only  two  cases  are  known  to  me  in  this  group — one  a  lizard  and  the 
other  a  turtle.  Jacquet  has  described  an  individual  {Lacerta  agilis) 
that  was  externally  a  male,  but  had  on  each  side  a  well-developed 
oviduct  that  was  attached  to  the  cloaca  at  one  end  and  opened  into 
the  body-cavity  at  the  other.     No  ovaries  were  present,  however. 

Fantham  has  described  a  turtle  (Testudo  grceca)  that  had  the 
external  characters  of  a  male.  The  concavity  of  the  plastron  was 
less  marked  than  in  a  normal  male.  It  had  on  the  left  side  an  ovo- 
testis, and  on  the  right  a  testis.  Two  ova  were  present  in  the  former. 
Such  a  condition  might,  as  suggested  above  for  the  Crustacea,  be 
imagined  to  be  due  to  chromosomal  elimination,  but  the  effect  here 
was  not  localized,  but  extended  beyond  the  ovotestis,  since  both  sets 
of  ducts  were  present. 

GYNANDROMORPHS  IN  BIRDS. 

The  division  into  males  and  females  is  sharply  drawn  in  the  groups 
of  birds,  although  in  some  families,  as  in  the  pigeons,  the  external 
differences  (the  secondary  sexual  differences)  may  be  slight,  while  in 
other  groups,  owing  to  the  development  of  secondary  sexual  characters, 
the  external  differences  are  very  striking.  In  still  other  forms  the 
secondary  sexual  characters  appear  only  at  certain  seasons  of  the 
year  and  disappear  largely  at  other  seasons.  The  five  cases  of  bilateral 
gynandromorphs  that  have  been  recorded  make  the  group  of  particular 
interest  in  the  present  connection,  while  the  exceptional  conditions 
shown  by  certain  hybrid  crosses  of  pheasants  call  for  careful  analysis, 
especially  in  connection  with  what  appears  to  be  at  least  an  analogous 
condition  in  hybrids  of  the  gipsy  moth. 

The  genetic  evidence  shows  very  explicitly  that  the  female  is  hetero- 
gametic,  the  male  homogametic.  The  sex-linked  inheritance  shown 
by  poultry  and  canaries  is  strictly  comparable  to  that  in  Drosophila, 
except  that  in  the  birds  the  male  has  two  Z  chromosomes  (or  ZZ)  and 
the  female  one  Z  (and  possibly  also  a  W,  i.  e.,  she  is  ZW).    The  cyto- 


102  THE    ORIGIN    OF    GYNANDROMORPHS. 

logical  evidence  that  can  be  adduced  in  support  of  this  view  is  not 
definitely  established. 

Guyer's  account  of  the  ripening  of  the  sperm  and  eggs  in  the  fowl 
is  as  follows:  In  the  male  there  are  18  chromosomes,  including  two 
Z  chromosomes.  After  sj^napsis  there  are  9  double  chromosomes  in 
the  first  spermatocytes,  all  of  which  except  the  double  Z  di\dde  (or 
separate),  9  going  to  one  pole,  8  to  the  other.  Thus  one  daughter 
cell  gets  both  Z's.  This  cell  divides  again,  the  Z's  presumably  separat- 
ing, so  that  two  second  spermatocytes  are  produced,  each  with  9  chro- 
mosomes (including  the  Z).  These  become  the  functional  sperm.  The 
other  daughter  cell  (without  the  Z's)  may  divide  again,  but  it,  or  its 
products,  degenerate. 

In  the  female  there  are  17  chromosomes,  including  one  Z.  Pre- 
sumably after  reduction  half  of  the  eggs  contain  a  Z  and  half  are 
without  it.  The  Z-bearing  egg  fertilized  by  any  sperm  (each  carries 
one  Z)  will  make  a  male  with  18  chromosomes,  including  two  Z's; 
the  egg  without  Z  fertilized  by  any  sperm  makes  a  female  with  17 
chromosomes,  including  one  Z.  The  scheme  will  account  for  the  sex- 
linked  inheritance  shown  by  the  fowl.  All  genes  carried  by  the  two 
sex  chromosomes  of  the  father  will  be  transmitted  to,  and  shown  by, 
his  daughters,  because  each  daughter  gets  her  single  sex  chromosome 
from  her  father.  If  the  male  carries  dominant  genes  in  his  sex  chromo- 
somes, both  daughters  and  sons  will  show  the  corresponding  dominant 
characters,  etc. 

It  is  important  to  observe  here  that  while  this  mechanism  gives  the 
same  results  as  to  sex  and  sex-linked  inheritance  as  the  mechanism 
described  by  Seller  for  moths,  the  actual  process  by  which  the  two 
end-results  are  reached  are  quite  different  in  the  male,  although 
presumably  the  same  in  the  female.  In  the  moth  the  reduction  has 
been  worked  out  both  in  the  male  and  female,  while  in  the  bird  only 
in  the  male. 

Five  cases  of  gynandromorph  have  been  described  in  birds,  four  of 
which  were  bilaterally  halved.^  Poll  described  a  bullfinch  that  had 
a  testis  on  the  right  side,  and  this  side  had  the  red  color  on  the  breast 
characteristic  of  the  normal  male ;  on  the  left  side  there  was  an  ovary, 
and  the  left  side  of  the  breast  was  gray  like  the  normal  female.  (See 
frontispiece  in  Doncaster's  book  on  The  Determination  of  Sex.) 

Weber  gives  a  full  account  of  a  finch,  Fringilla  coelehs,  that  had 
the  adult  male  plumage  on  the  right  side  and  that  of  the  female  on 
the  left  side.  The  left  side  contained  an  ovary,  the  right  a  testis. 
Weber  states  that  Cabanis  (Journ.  fiir  Ornithologie,  XXII,  1874) 
describes  a  "Dompfaffen"  {Pyrrhula  vulgaris)  that  was  a  bilateral 
gj^nandromorph — on  the  right  side  male,  on  the  left  female.     The  bird 

^  Several  mixed  cases  in  hybrid  pheasants  and  in  Tetrao  lestrix  have  been  omitted  here,  as 
well  as  references  to  "hermaphroditic"  fowls. 


THE    ORIGIN    OF   GYNANDROMORPHS.  103 

was  not  dissected.  He  records,  apparently  also  on  the  authority  of 
Cabanis,  another  bilateral  gynandromorph  in  the  species  Cola-pies 
mexicanus.  Here,  curiously  enough,  the  right  half  was  female,  the 
left  male,  but  Weber  suggests  that  possibly  the  bird  had  the  adult 
male  plumage  on  the  left  side,  while  on  the  right  the  plumage  was  juve- 
nile; in  other  words,  the  bird  was  a  male,  but  with  the  full  plumage  only 
on  one  side,  and  that  the  left  side,  which  normally  contains  the  ovary. 

Brandt  states  that  Lorenz  found  in  the  markets  of  Moscow,  in  the 
course  of  fifteen  years,  three  male  Tetrao  tetrix  with  female  plumage; 
one  of  these  had  a  testis  on  one  side  and  an  ovary  on  the  other. 

Bond  has  described  a  pheasant  with  the  plumage  of  the  left  side 
preponderantly  male,  that  of  the  right  side  preponderantly  female. 
On  the  left  side  there  was  an  ovary,  and  this  is  the  normal  position  of 
the  ovary  in  birds.  It  contained  both  ovarian  and  testicular  tissue. 
There  was  no  trace  of  a  gonad  on  the  right  side.  In  the  last  three  cases 
there  is  no  stated  correspondence  between  the  external  and  the 
internal  division  of  the  sexes. 

Setting  aside  the  two  rather  doubtful  cases  (that  of  Cabanis  and  the 
uncertain  reference  to  Lorenz's  case),  there  remain  the  two  well- 
established  cases  of  Poll  and  Weber,  where  dissection  was  made,  and 
Bond's  case,  that  is  like  the  last,  but  not  so  clear,  since  the  ovary 
contained  also  testicular  tissue. 

It  is  very  difficult  to  explain  these  cases  by  chromosomal  elimina- 
tion, even  if  the  male  and  female  plumage  differences  were  supposed 
to  be  due  to  two  or  one  (Z)  chromosomes  in  the  parts  affected.  Start- 
ing as  a  male  with  two  Z  chromosomes,  if  one  were  lost  at  an  early 
division  one  half  of  the  bird  would  be  female,  Z,  and  the  other  male, 
ZZ.  This  possibility  could  be  established  only  by  finding  a  bilateral 
gynandromorph  in  a  hybrid  that  was  heterozygous  for  sex-linked 
factors.  Such  factors  have  been  described  for  pigeons  (Cole  and 
Staples-Browne)  and  for  doves  (Strong,  R.  M.,and  Riddle),  for  canaries, 
and  for  fowls,  but  no  cases  of  gynandromorphs  in  them  have  yet  been 
met  with  in  which  these  characters  were  involved. 

An  attempt  to  bring  the  avian  results  in  line  with  the  Drosophila 
runs  counter  to  the  evidence  from  gonadectomy,  since  it  assumes 
that  the  differences  involved  are  due  directly  to  the  chromosomal 
composition  of  the  male  and  the  female  parts,  and  are  not  due  to 
ovarian  extract,  which,  in  poultry  and  ducks  at  least,  has  been  shown 
to  suppress  in  the  female  her  potentiality  of  developing  the  full  cock 
plumage.  It  may  be  interesting  to  review  briefly  this  situation,  since 
Goodale's  results  with  ducks  show  that  the  relation  of  the  plumage 
to  the  gonad  is  not  so  simple  as  appeared  at  first. 

It  has  long  been  known  in  poultry  that  the  removal  of  the  testes 
does  not  interfere  with  the  development  of  the  secondary  sexual 
plumage  of  the  cock.     In  color,  shape,  and  size  of  the  feathers  the  capon 


104  THE    ORIGIN   OF   GYNANDROMORPHS. 

is  very  similar  to  the  normal  cock.  The  comb  and  wattles,  however, 
are  greatly  reduced  in  size  and  have  a  pale  color,  being  relatively 
deficient  in  blood.  The  influence  of  castration  on  the  spurs  is  not  clear, 
for  they  may  be  well  developed  in  the  capon  and  even  in  the  hen. 
The  influence  of  the  ovary  on  the  plumage  of  the  hen  has  long  been 
suspected  to  be  important.  Old  hens  in  which  the  ovary  had  ceased 
to  function  were  known  to  develop  cock  feathering,  and  the  same 
result  was  said  to  follow  if  the  ovary  became  diseased.  But  much 
uncertainty  existed  in  regard  to  this  evidence  until  Goodale,  by  care- 
fully planned  and  thorough  work,  showed  that  when  the  ovary  was 
removed  from  young  birds  they  developed  the  complete  plumage  of 
the  male.  In  the  race  of  Leghorns  the  cock  is  red  with  plumage  like 
that  of  the  wild  Gallus  hankiva;  the  hens  are  brown.  After  spaying, 
the  hens  develop  the  complete  male  plumage.  The  spurs  develop  more 
fully  than  in  the  normal  female  of  the  Leghorn  race. 

When  pieces  of  the  ovary  of  a  Leghorn  hen  were  inserted  in  the 
body-cavity  of  a  Leghorn  capon,  the  latter  developed  only  the  female 
plumage. 

In  domesticated  ducks  (Rouen  and  Mallard)  there  are  two  molts. 
The  drake  molts  in  June  and  assumes  his  summer  plumage,  which  is 
more  like  that  of  the  female  than  is  his  other  so-called  nuptial  plumage. 
The  nuptial  plumage  develops  during  the  autumn  molt.  If  the  testes 
are  completely  removed  after  the  autumn  molt  the  male  retains  his 
nuptial  plumage  even  through  the  summer  molt.  Goodale  finds  that 
in  normal  birds,  when  the  summer  plumage  reaches  its  highest  stage 
of  development,  sexual  activity  diminishes  or  disappears,  and  few  or 
no  sperms  are  present.  It  is  at  this  time  then  that  the  drake  de- 
velops his  nuptial  plumage,  as  removal  of  feathers  shows  In  other 
words,  it  is  the  summer  plumage  (the  one  that  is  more  like  the  female) 
that  develops  when  the  sexual  organs  are  at  the  highest  development, 
while  the  nuptial  plumage  develops  when  the  sperms  are  not  being 
produced  in  the  testes.  It  appears,  then,  that  the  nuptial  plumage 
is  not  influenced  by  the  testicular  condition,  while  the  female-like 
plumage  may  possibly  be  due  to  the  inhibitory  eff'ects  of  the  testicular 
secretions.  In  other  words,  the  case  is  somewhat  like  that  of  the 
Sebright,  in  which  the  presence  of  the  active  testis  suppresses  the 
potential  cock  feathering  of  the  male. 

These  results  do  not  appear  to  furnish  any  solution  of  the  problem 
of  bilateral  gynandromorphs  in  birds,  because  the  chief  difficulty 
remains  so  long  as  any  internal  secretion,  whether  ovarian  or  testicular, 
determines  in  an  individual  the  character  of  its  plumage.  Any  theory 
of  bilateral  gynandromorphs  in  birds  must  be  prepared  to  offer  some 
explanation  as  to  why  the  ovarian  extracts  do  not  suppress  in  them 
the  male  feathering  on  the  male  side.  Two  more  or  less  plausible 
answers  can  be  given  at  present.     One  of  them  is  that  in  certain 


THE    ORIGIN    OF   GYNANDROMORPHS.  105 

species  of  birds  the  male  plumage  is  not  affected  by  ovarian  secretions, 
as  it  is  in  poultry  and  in  ducks,  but  is  due  directly  to  genetic  factors 
that  act  effectively  in  the  male  but  not  in  the  female.  It  ought  to 
be  comparatively  easy  to  find  this  out  for  each  race  by  means  of 
gonodectomy. 

The  other  possible  explanation  is  that  although  in  a  bird  genetically 
male  (ZZ)  on  one  side  and  female  (Z)  on  the  other,  the  secondary 
sexual  characters  would  be  female;  yet  if  the  ovary  should  become 
diseased  or  old  and  its  secretions  diminished,  a  point  might  be  reached 
where  the  secretion  could  no  longer  hold  in  check  the  full  develop- 
ment of  the  male  part.  The  bilateral  gynandromorph  in  birds  would 
on  this  view  represent  only  a  transient  stage.  In  point  of  fact,  none 
of  them  have  been  kept  alive  for  any  length  of  time,  so  that  we  do 
not  know  that  they  would  hold  their  superficial  peculiarity.  An 
alternative  to  this  view  that  the  secretions  were  insufficient  because 
of  disease  or  age  is  to  suppose  that  the  ovary  is  abnormally  small 
from  accident  or  heredity.  In  this  case  the  gynandromorph  stage 
would  be  more  permanent.  Such  birds  would  be  expected  in  all  cases 
to  have  an  ovary,  or  at  least  to  have  some  traces  of  one,  unless  the 
species  resembled  Mallards  or  Sebrights,  where  the  testis  influences  the 
plumage. 

The  results  that  Riddle  has  reported  concerning  intersexes  in  hybrid 
pigeons  do  not  call  for  detailed  review  here,  since  the  phenomena 
recorded  relate  largely  to  behavior.  Riddle  believes  that  under 
"conditions  of  overwork"  a  female  produces  eggs,  some  of  which  are 
male-producing,  others  female-producing,  as  shown  by  mating  such 
females  to  the  males  of  their  own  species  when  equal  numbers  of 
males  and  females  are  produced.  But  such  overworked  eggs,  if  fertil- 
ized by  a  male  of  a  different  genus,  produce  predominantly  female  birds. 
The  result,  however,  is  not  attributed  to  the  male,  or  to  the  cross,  but 
to  some  change  in  the  egg  that  causes  a  reversal  of  the  sex  tendency. 

The  only  case  that  Riddle  has  reported  in  which  the  color  inheritance 
is  given,  so  that  one  can  follow  the  sex-linked  heredity  in  connection 
with  the  abnormal  sex  ratio,  is  that  recorded  in  the  Naturalist  for 
1916.^  The  first  17  doves  were  5  male  to  12  female  doves;  the  second 
17  doves  were  4  males  to  13  females;  the  last  17  doves  were  2  males  to 
15  females.  The  cross  was  made  between  Streptopelia  alba  male 
and  St.  risoria  female.  As  R.  M.  Strong  had  previously  shown,  the 
expectation  here  is  for  dark  sons  and  white  daughters.  Since  the 
reciprocal  cross  gives  all  dark  offspring,  the  factor  involved  is  sex- 
linked  and  not  merely  sex-limited.  Riddle  obtained  only  dark  males 
and  white  females,  except  two  that  were  dark  (one  being  questioned 
by  himself).  Strong  also  found  a  few  dark  exceptions,  as  did  also 
Staples  Brown.      As  Bridges  has  showai,   these  exceptions   can  be 

'  Reproduced  and  expanded  in  the  Journal  of  the  Washington  Academy  of  Sciences,  June  1917. 


106  THE    ORIGIN   OF   GYNANDROMORPHS. 

explained  by  non-disjunction.  They  are  too  few  in  any  case  to  affect 
Riddle's  argument  based  on  the  sex-ratio.  It  follows,  then,  that 
Riddle's  results,  instead  of  showing  that  some  females  started  as  males, 
show  exactly  the  reverse,  since  the  genetic  history  shows  that  all  his 
females  must  have  had  the  genetic  chromosome  constitution  character- 
istic of  the  female  and  have  gotten  it  in  the  usual  way. 

GYNANDROMORPHS  IN  MAMMALS-MAN. 

Cases  of  true  hermaphroditism  or  gynandromorphism  in  mammals 
and  in  man  are  extremely  rare.  From  the  meager  evidence  it  is  not 
clear  whether  the  cases  reported  belong  under  one  or  the  other  head, 
but  there  are,  as  far  as  we  know,  very  few  if  any  cases  of  strictly 
bilateral  gynandromorphs.  The  secondary  sexual  differences,  while 
not  so  marked  as  in  some  other  groups,  are  yet  sufficient,  one  would 
suppose,  to  make  a  bilateral  type  clearly  evident.  Goldschmidt  has 
suggested  that  intersexes  occur  in  man  of  the  kind  shown  by  the  gipsy 
moth.  So  far,  at  least,  there  is  no  positive  evidence  to  show  that  such 
individuals  occur  more  frequently  in  racial  crosses  in  man  than  within 
the  race,  but  the  human  races  are  themselves  so  mixed  in  origin  that 
this  point  may  not  have  any  critical  value  for  the  subject.  A  priori, 
it  is  equally  possible  that  the  intersexual  individuals,  if  genetic  ones 
exist,  may  be  due  to  autosomal  differences  that  affect  the  normal 
instincts  rather  than  to  differences  in  the  sex  genes  themselves.  It  is  not 
claimed,  I  believe,  that  the  actual  sex-organs  themselves  are  involved, 
but  rather  secondary  sexual  characters  and  instincts  whose  relation  to 
the  sex  mechanism  are  in  man  entirely  obscure. 

According  to  Rudolphi,  there  is  a  record  by  Schlumpf  (Arch.  f. 
Thierheilkunde,  Zurich,  1824,  pp.  204-206)  of  a  calf  externally  like  a 
male,  but  in  place  of  the  scrotum  there  are  present  the  udders  with  the 
usual  number  of  nipples.  The  uterus  had  only  one  horn  and  funnel, 
and  an  ovary  fastened  to  right  side  of  "der  Leiden."  To  one  kidney 
(left)  was  attached  a  small  testis.  Rudolphi  also  describes  a  seven 
weeks'  old  child  that  lived  about  three  months  that  had  a  hypospadic 
penis  and  in  the  right  scrotum  a  testis,  but  no  testis  in  the  left.  There 
was  a  uterus  whose  left  upper  end  was  connected  with  a  Fallopian 
tube  attached  to  which  was  an  ovary.  On  the  right  side  the  uterus 
ended  blindly  and  there  was  neither  Fallopian  tube  nor  ovary  present. 
Two  very  similar  cases,  one  by  Gautier  (1752)  and  one  by  Pinel,  are 
referred   to  by  Rudolphi.^ 

According  to  Pick  (1914),  Sauerbeck  admits  only  7  cases  of  her- 
maphrodites in  mammals  as  certain  and  complete,  5  for  swine,  and  2 
for  man  (Salens,  1899,  and  Simon,  1903),  to  which  number  are  added  3 

^Rudolphi  (1825)  refers  to  two  supposed  cases  of  hermaphrodites  in  fowls,  which  he  very 
properly  questions. 


THE    ORIGIN    OF   GYNANDROMORPHS. 


107 


-Vas. 


Text-figure  70. 


cases  for  mammals  (roebuck  and  goat)  and  5  for  man  as  verj'  probable. 
To  these  Pick  adds  a  later  case  by  Uffreduzzi  (1910)  and  one  by 
Gudernatsch  (1911).  The  5  cases  found  in  swine  by  Pick  are  of 
unusual  interest.  The  external  genitalia  were  entirely -female  or  nearly 
so.  Within  the  abdomen  were  uterus  and  fallopian  tubes  (text-fig. 
70) .     In  four  of  the  cases  an  ovotestis  was  present  on  each  side  in  the 

normal  position  of  the  ovary.    In 
the  fifth  case  an  ovary  with  a 
small  piece  of  testis  was  on  one 
side  and  a  testis  on  the  other. 
The  conditions  here  suggest  at 
least  that  the  results  are  not  due 
to  chromosomal 
elimination,  al- 
though such  an 
interpretation 
might  be  given. 
If,  for  instance, 
the  gonads  arise 
at  an  early  stage 
froma  single  cell 

in  which  an  anterio-posterior  division  occurred  and  the  later  mass  of 
cells  was  subsequently  separated  into  right  and  left  parts,  the  condi- 
tions found  might  be  realized.  There  is,  however,  a  possibility  that 
here,  as  in  cattle,  a  \mion  between  the  chorions  of  the  embr\'o  in  the 
uterus  might  have  brought  about  a  more  perfect  freemartin  than 
develops  in  cattle  when  such  a  union  occurs.     (See  Lillie.) 

Ritter  described  a  pig  in  which  on  the  right  side  a  testis  was  present 
and  on  the  left  an  ovary.  (Verh.  phys.  Med.  Gesell.  Wiirzburg,  XIX, 
1886).  Harman  more  recently  (1917)  describes  a  cat  with  a  testis 
on  one  side  and  an  ovary  on  the  other.  Neurgebauer  has  given  a 
large  number  of  cases  in  man  in  w^hich  testes  and  ovaries  have  been 
described  in  the  same  individual  and  in  which  the  genitalia  show  many 
anomalous  relations.  Amongst  the  large  number  of  human  hermaph- 
rodites described  there  are  probably  a  considerable  number  of 
authentic  cases  where  parts  of  both  male  and  female  genitalia  were 
combined  in  the  same  individual,  but  writing  as  late  as  1911,  Guder- 
natsch states  that  hermaphroditism  in  the  sense  of  separate  ovaries 
and  testes  has  not  been  demonstrated  in  man.  He  describes  a  case 
of  an  individual  with  female  external  genitalia  and  an  abnormal  testis 
in  the  right  inguinal  canal. 

The  proof  that  hermaphroditism,  so-called,  in  man  is  produced  in 
the  same  way  as  gynandromorphism  in  Drosophila  can  not  be  furnished 
at  present,  because  there  is  no  probability  of  the  difference  in  chromo- 
some number  being  determined  by  histological  study,  owing  to  the 


108  THE    ORIGIN   OF   GYNANDROMORPHS. 

large  number  of  chromosomes,  nor  is  it  probable  that  a  case  involving 
sex-linked  factors  will  soon  be  found. 

Some  of  the  older  writers  seem  to  mean  by  hermaphroditism  the 
presence  of  complete  sets  of  both  male  and  female  organs,  the  two 
systems  superimposed  on  each  other.  The  rather  mythical  accounts 
of  such  cases  do  not  call  for  serious  comment.^  Where  the  evidence 
is  anatomical  and  given  by  trained  observers  it  appears  that  some, 
perhaps  all,  cases  are  mosaics  rather  than  "hermaphrodites"  in  the 
sense  of  double-sexual  individuals.  In  other  words,  parts  of  one  and 
parts  of  another  system  are  found  in  the  same  individual,  replacing 
each  other  locally.  If  this  interpretation  turns  out  to  cover  certain 
cases  the  theory  of  chromosomal  elimination  will  suffice  at  least  as  a 
formal  explanation  of  such  human  abnormalities.  Since  the  human 
species  is  both  from  the  genetic  and  cytological  evidence  XX  in  the 
female  and  XO  in  the  male,  the  same  mechanism  exists  as  is  found  in 
Drosophila,  and  if  the  theory  of  chromosomal  elimination  applies  here 
also,  human  gynandromorphs  would  be  expected  in  practically  all 
cases  to  begin  as  female  (XX)  and  produce  male  regions  by  eliminat- 
ing one  X.  An  examination  of  the  literature  shows  in  fact  a  consider- 
able preponderance  of  the  cases  showing  more  female  than  male  regions, 
but  the  evidence  is  too  uncertain  to  give  any  serious  weight  to  it. 

IS  CANCER  A  SOMATIC  MOSAIC? 

Into  the  difficult  and  obscure  question  as  to  the  cause  of  cancer  it 
is  not  our  business  to  enter,  but  a  suggestion  made  by  Boveri  (in 
1902  and  1914)  calls  for  brief  notice,  since  he  appealed  to  a  process 
akin  to  chromosome  elimination  as  a  possible  explanation  of  the 
phenomenon.  Boveri  suggested  that  an  imperfect  or  irregular  division 
of  the  chromosomal  complex  might  in  certain  cases  produce  combina- 
tions through  loss  of  specific  chromosomes  that  caused  the  different 
cells  to  run  wild,  so  to  speak,  in  the  sense  that  factors  that  normally 
inhibit  the  rate  of  growth  or  the  suppression  of  growth  in  relation  to 
the  cell  environment  are  lost.  In  support  of  such  a  view  he  appealed 
to  occupational  cancer-growth,  where  cancer  develops  in  parts  of  the 
body  most  subject  to  mechanical  injury  or  pressure.  It  is  known  to 
students  of  embryology  that  compression  of  a  dividing  cell  may  inter- 
fere with  the  normal  distribution  of  the  chromosomes  to  the  daughter 
cells.  At  present,  however,  reference  to  such  possible  sources  is  too 
uncertain  to  be  of  great  value,  for  there  are  no  instances  where  irregu- 
larities of  this  kind  are  known  to  give  rise  to  prolific  growth  processes. 
The  cancer-like  or  tumor-like  growth  shown  by  a  mutant  race  of 
Drosophila,  discovered  by  Bridges  and  described  fully  by  Stark,  has 
not  been  shown  to  be  associated  with  abnormal  distribution  of  the 

'  See  comment  by  Dr.  H.  L.  Garrigues,  Medical  Record,  1896,  p.  725. 


THE    ORIGIN    OF   GYNANDROMORPHS.  109 

chromosomes,  although  this  point  has  not  been  sufficiently  studied  to 
exclude  such  a  process.  On  the  other  hand,  it  has  been  shown  that 
the  growth  in  question  is  caused  by  a  sex-linked  Mendelian  gene  that 
is  inherited  strictly,  as  are  all  Mendelian  sex-linked  genes.  This 
mutant  lethal  race  of  Drosophila  arose  as  a  mutation,  presumably  in 
the  same  way  as  other  mutations.  If  it  is  not  admissible  at  present 
to  draw  any  analogy  between  this  case  and  that  of  mammalian  cancer, 
it  is  conceivable  at  least  that  mammalian  cancer  may  be  due  to  re- 
current somatic  mutation  of  some  gene.  Such  a  conclusion  would, 
however,  not  invalidate  the  view  that  cancer  is  more  likely  to  occur 
in  certain  families,  or  even  be  inevitable  in  them,  because  recurrent 
mutation  in  certain  genes  appears  to  be  more  likely  than  in  other 
genes.  But  even  if  this  view  were  maintained  the  inheritance  would 
be  different  in  kind  from  the  inheritance  of  ordinary  Mendelian  genes, 
because  such  a  view  involves  a  secondary  step,  viz,  the  likelihood  of 
a  mutation  in  a  race  containing  the  inherited  gene  in  question.  The 
whole  problem  of  the  causes  of  mutation  is  at  present  so  obscure  that 
a  discussion  of  this  possibility  is  purely  theoretical.  Added  to  this 
is  the  uncertainty  of  how  cancer  is  inherited  in  those  races  of  mice 
that  appear  to  produce  it  with  great  frequency.  Important  as  the 
work  along  these  lines  unquestionably  is,  the  subject  is  not  yet  ripe 
for  any  positive  statement.  It  may,  nevertheless,  be  worth  while  to 
keep  in  view  the  possibility  suggested  above,  viz,  that  what  is  in- 
herited in  cancer  may  be  a  gene  or  complex  of  genes  in  which  somatic 
mutation  is  of  sufficient  frequency  to  give  the  appearance  that  a  gene 
for  cancer  is  itself  inheritable. 

IS  THE  FREEMARTIN  A  GYNANDROMORPH? 

It  has  been  suggested  that  the  pair  of  twin  calves,  one  male,  the  other 
a  sterile  female  (the  freemartin),  together  represent  a  sort  of  gynandro- 
morph.  This  view  is  based  on  the  assumption  (which  Lillie  has  since 
disproven)  that  these  twins  arise  from  a  single  egg.  Hart  (Proceed- 
ings Roy.  Soc.  Edinburg,  XXX,  p.  218)  suggested  that  "the  free- 
martin  with  a  potent  bull  twin  is  the  result  of  a  division  of  a  male 
zygote,  so  that  the  somatic  determinants  are  equally  divided  and  the 
genital  determinants  unequally  divided,  the  potent  going  to  one  twin, 
the  potent  bull,  the  non-potent,  genital  determinant  to  the  free- 
martin."  It  is  needless  to  point  out  that  this  vague  statement  can 
not  be  brought  into  accord  with  embryological  evidence,  because 
Lillie 's  work  shows  that  each  individual  of  the  twins  arises  from  a 
separate  egg.  In  most  cases  the  eggs  arise  from  the  two  ovaries,  and 
each  embryo  lies  in  a  different  horn  of  the  uterus. 

Lillie  has  shown  that  in  those  cases  where  twins  are  present,  one  of 

which  is  a  freemartin,  the  two  chorions  and  the  two  allantois  have 

I  fused  at  an  early  stage,  and  he  has  demonstrated  that  there  is  an 


110  THE    ORIGIN   OF   GYNANDROMORPHS. 

actual  vascular  connection  between  the  two  individuals.  There  can 
remain  no  doubt  that  the  results  are  due  to  the  estabhshment  of  a 
common  circulation.  Lillie  brings  very  strong  evidence  in  favor  of  the 
view  that  the  freemartin  starts  as  a  normal  female.  The  failure  of 
her  ovary  to  develop,  he  thinks,  is  due  to  a  sex  hormone  (see  below) 
that  originates  in  the  testis  of  the  male  and  suppresses  the  normal 
development  of  the  ovary.  The  external  genitalia  of  the  freemartin, 
and  to  some  extent  the  uterus  and  ducts,  are,  as  a  rule,  less  affected  by 
the  hormone,  so  that  externally  the  freemartin  appears  to  be  a  female. 
Even  more  remarkable  is  the  fact  that  the  male  ducts  are  sometimes 
quite  well  developed  and  the  development  of  the  ovary  appears  to 
take  in  somewhat  the  characteristic  changes  seen  in  the  development 
of  the  testis.  This  conclusion  is  based  largely  on  the  results  of  a  histo- 
logical examination  by  Miss  C.  L.  Chapin.  Lillie  is  not  inclined,  how- 
ever, to  lay  very  much  emphasis  on  this  side  of  the  question,  because, 
as  he  states,  the  suppression  of  the  ova  (and  female  stroma?)  may  in 
itself  allow  some  of  the  male  characteristics  to  develop  to  a  stage  not 
normally  present  in  the  female.  In  other  words,  the  development  of 
the  accessory  organs  may  to  a  certain  extent  be  under  the  influence  of 
the  gonad. 

The  assumption  of  a  male  hormone  originating  in  the  interstitial 
cells  of  the  testis  is  more  problematical.  The  only  fact  advanced  by 
Lillie  in  favor  of  this  interpretation  is  that  in  the  testis  the  interstitial 
tissue  develops  at  an  earlier  stage  than  that  in  the  ovary.  It  is  true 
that  there  is  also  some  evidence  indicating  that  the  interstitial  cells  of 
the  testis  produce  some  substance  that  affects  the  secondary  sexual 
characters  of  the  male.  But  it  may  be  that  other  substances  in  the 
blood  of  the  male  affect  the  ovary  of  the  freemartin  and  retard  its 
development.  Such  substances  might  also  be  called  hormones,  but 
have  no  direct  relation  either  to  the  development  of  the  germ-cells 
in  the  testes  or  to  sex  determination  in  any  specific  sense.  If  in  cattle 
the  male  differs  from  the  female  by  one  sex  chromosome,  it  is  quite 
possible  that  the  composition  of  the  blood  of  the  male  is  different  in 
some  substances  (or  relative  proportion  of  substances)  from  the  blood  of 
the  female.  The  difference,  while  the  product  of  sex  in  the  sense 
that  all  the  body-cells  of  the  male  differ  by  one  chromosome  from  the 
body-cells  of  the  females,  might  not  in  any  way  be  connected  with 
sex  determination,  even  although  it  affected  injuriously  the  develop- 
ment of  the  ovary  of  the  young  female  embryo.  Until  further  evidence 
is  obtained,  the  source  of  the  "hormone"  that  affects  the  freemartin 
must  remain  an  open  question. 

If  the  ovary  of  the  freemartin  is  actually  changed  to  a  testis  it  may 
be  said  that  the  freemartin  is  a  sex  mosaic,  the  external  genitalia  female 
and  the  gonads  more  or  less  male.  The  cause  of  such  a  sex  mosaic 
would,  then,  obviously,  be  entirely  different  from  the  cause  of  the 
gynandromorphs  of  Drosophila. 


THE    ORIGIN   OF   GYNANDROMORPHS.  Ill 

SUMMARY. 

(1)  (a)  The  main  outcome  of  this  work  on  gj'nandromorphs  of 
Drosophila  is  an  experimental  demonstration  of  the  principal  cause  of 
the  regional  differences  that  gives  rise  to  the  coml)inations  of  male  and 
female  in  the  same  individual.  The  demonstration  was  made  possible 
by  taking  advantage  of  the  genetic  situation  in  this  material. 

(b)  Many  of  the  gynandromorphs  were  hybrids  of  known  sex-linked 
characters,  i.  e.,  characters  whose  genes  are  carried  by  the  sex 
chromosomes. 

(c)  By  adding  to  such  crosses  additional  characters  whose  genes  lie 
in  other  than  the  sex  chromosomes  it  has  been  possible  to  prove  that 
the  male  and  female  parts  of  the  gynandromorph  differ  by  the  sex 
chromosomes  alone,  i.  e.,  both  male  and  female  parts  contain  the  same 
autosomal  group. 

(d)  It  was  possible,  in  consequence,  to  show  that  these  gynandro- 
morphs are  not  due  to  partial  fertilization  (Boveri),  or  to  polyspermy 
(Morgan),  but  to  chromosoma,l  elimination  (Morgan).  Chromosomal 
ehmination  means  that  at  an  early  stage  in  embryonic  development 
one  of  the  daughter  chromosomes  of  one  of  the  X's  fails  to  pass  over 
to  one  of  the  daughter  plates,  and  accordingly  gets  left  out  of  that 
nucleus.  In  consequence,  one  of  the  two  cells  will  contain  only  one 
X  chromosome  and  produce  male  parts,  while  the  sister  cell  with  two 
daughter  X  chromosomes  will  produce  female  parts.  The  evidence 
that  elimination  of  this  kind  takes  place  rests  on  cases  in  which  the 
X  chromosome  derived  from  the  father  contains  different  sex-linked 
genes  from  the  X  chromosome  derived  from  the  mother. 

(e)  A  census  of  the  available  gynandromorphs  shows  that  a  paternal 
X  chromosome  is  eliminated  as  often  as  a  maternal  X  chromosome. 

(2)  A  logical  consequence  of  the  proof  that  the  gynandromorphs 
arise  through  elimination  is  that  they  should  all  start  as  females, 
i.  e.,  as  XX  individuals.  If  the  elimination  always  takes  place  at  the 
first  division  the  expectation  would  be  for  the  male  and  female  parts 
to  be  equal;  but  if  at  the  second,  third,  or  any  later  division  of  the 
nuclei,  we  should  expect  to  find,  on  the  whole,  a  preponderance  of 
female  parts  over  male  parts.     Such  is  strikingly  the  case. 

(3)  A  second  logical  consequence  of  chromosomal  elimination  is 
that  starting  as  an  XX  individual;  the  male  parts  will  be  XO,  and  not  > 
XY  as  in  the  normal  male.     Now,  it  has  been  shown  by  Bridges  ' 
(191G)  that  XO  males  arising  from  primary  non-disjunction  are  sterile  : 
(although  in  structure,  etc.,   they  are  exactly  like  XY  or  normal  ' 
males).     The  great  majority  of  gynandromorph  individuals  with  male 
abdomen  and  testes  are  infertile,  while  if  the  corresponding  parts  are 
female  the  individual  is  fertile.     The  few  gynandromorphs,  fertile  as 
males,  are  known  from  other  genetic  evidence  to  have  come  from  XXY 


112  THE    ORIGIN   OF   GYNANDROMORPHS. 

mothers  or  to  be  themselves  XXY  zygotes.  In  such  cases,  after  elimi- 
nation, the  male  parts  are  expected  to  be  XY,  and  hence  an  individual 
of  this  origin  with  a  male  abdomen  and  testes  is  expected  to  be  fertile. 

(4)  A  striking  fact  in  regard  to  these  gynandromorphs  is  that  the 
male  and  female  parts  and  their  sex-linked  characters  are  strictly 
self -determining,  each  developing  according  to  its  own  constitution. 
No  matter  how  large  or  how  small  a  region  may  be,  it  is  not  interfered 
with  by  the  aspirations  of  its  neighbors,  nor  is  it  overruled  by  the 
action  of  the  gonad. 

(5)  Four  experiments  were  made  in  which  suitable  material  was 
carefully  scrutinized  for  gynandromorphs.  In  the  88,000  flies,  there 
were  found  40  gynandromorphs,  or  1  to  2,200.  Since  only  those  that 
start  as  females  give  this  kind  of  gynandromorph,  chromosomal 
elimination  may  have  occurred  once  in  1,100  individuals. 

(6)  (a)  If  chromosomal  elimination  took  place  at  the  first  division 
of  the  segmentation  nucleus,  a  half-and-half  gynandromorph  is 
expected  (right-and-left  or  anterio-posterior) .  Whether  dorso-ventral 
separation  is  expected  for  such  a  division  depends  on  whence  comes  the 
material  that  ultimately  reaches  the  dorsal  surface  of  the  fly. 

(6)  If  the  chromosomal  elimination  took  place  at  the  second-division 
period  in  one  of  the  nuclei  only  a  quadrant  is  expected  to  be  male,  etc. 

(c)  The  fact  that  most  of  our  mosaics  include  large  regions  of  the 
body  may  mean  that  elimination  takes  place  more  often  during  the 
first  or  second  division,  but  it  may  also  mean  that  when  smaller  regions 
are  involved  the  gynandromorph  would  be  more  often  overlooked. 

(7)  (a)  Both  gonads  of  the  same  individual  are  always  alike,  i.  e., 
both  are  testes  or  both  are  ovaries,  even  when  the  external  markings 
of  the  abdomen  are  male  on  one  side,  female  on  the  other.  This 
result  finds  its  explanation  in  the  assumption  that  the  germ-plasm 
of  Drosophila,  as  in  some  other  flies,  arises  from  a  single  cell.  This 
cell,  arising  after  elimination,  must  be  either  a  spermatogonium  or 
oogonium.  If  the  cell  be  the  former  the  sex-linked  factor  of  the 
germ-plasm  must  be  that  of  the  male-determining  X  chromosome 
alone  and  not  show  any  of  the  factors  contained  in  the  other  X  of  the 
female  parts.     Such  is  the  case. 

(h)  Conversely,  the  ovary  of  a  gynandromorph  containing  both  X 
chromosomes  should  produce  eggs  containing  the  original  X  chromo- 
somal combinations  as  well  as  their  cross-over  combinations.  This, 
too,  is  the  case. 

(8)  It  is  a  striking  fact  that  we  have  found  so  few  cases  of  autosomal 
elimination.  The  lack  of  such  mosaics  may  be  due  to  the  failure  of 
the  ordinary  chromosome  to  lag  in  division  as  the  X  is  assumed  to  do, 
or  it  may  be  that  a  fly  or  part  of  a  fly  can  not  exist  if  one  autosome 
is  absent  from  its  complex.  That  a  part  may  exist  with  one  X  chromo- 
some lost  might  be  explained  as  due  to  that  condition  having  been 


THE    ORIGIN   OF   GYNANDROMORPHS.  113 

already  acquired  by  the  male.     Future  work  must  show  whether  or 
not  such  autosomal  mosaics  are  viable. 

(9)  Courtship  has  been  watched  in  a  number  of  flies  that  were  partly 
male  and  partly  female.  Many  of  them  are  indifferent;  some  react  as 
males,  some  as  females. 

(10)  In  several  cases  flies  that  had  one  white  eye  and  one  red  eye 
have  been  observed  to  show  circus  movements.  Since  the  white- 
eyed  fly  is  less  responsive  to  light  than  the  red-eye  fly,  the  circus  move- 
ments of  the  gynandromorph  with  one  white  and  one  red  eye  is  what 
is  to  be  expected.  Of  course,  such  cases  must  be  selected  so  that  the 
legs  are  not  male  on  one  side  and  female  on  the  other. 

(11)  The  general  evidence  from  mutation  in  Drosophila  makes  it 
highly  probable  that  when  a  mutation  occurs  it  takes  place  in  only 
one  chromosome  of  the  pair.  Hence  any  mutation  in  somatic  tissue,  if 
recessive,  would  be  concealed  by  the  presence  of  the  normal  allelomorph 
in  the  homologous  chromosome.  If,  however,  a  mutation  should  appear 
in  the  sex  chromosome  of  the  male,  even  though  recessive,  its  efi'ects 
might  be  apparent.  It  is  probably  significant  that  the  ten  cases  here 
described  and  supposed  to  be  somatic  mutations  are  all  males. 

(12)  Theoretically,  at  least,  there  is  the  possibility  that  an  indi- 
vidual startiftg  as  a  male  might  produce  female  parts.  If  at  some 
embryonic  division  both  daughter  X's  of  an  XY  cell  should  pass 
into  the  same  cell,  it  would  be  expected  to  produce  female  parts.  There 
is,  however,  a  difficulty  with  the  other  cell  containing  a  Y  chromosome 
and  no  X.     It  would  probably  die. 

(13)  In  addition  to  the  two  earlier  theories  of  Boveri  and  Morgan 
mentioned  above,  other  theories  are  critically  considered  from  the  point 
of  view  of  the  gynandromorphs  of  Drosophila.  The  only  other  theory 
besides  elimination  that  we  have  found  necessary  to  employ  in  ac- 
counting for  the  gynandromorphs  of  Drosophila,  where  the  genetic  evi- 
dence makes  the  analysis  possible,  is  the  theory  of  binucleated  eggs. 

(14)  In  the  light  of  the  evidence  from  Drosophila, both,  the  Eugster- 
bee  gynandromorph  and  von  Engelhardt's  gynandromorph  can  be 
accounted  for  on  the  hypothesis  of  chromosomal  elimination,  especially 
since  the  work  of  Newell  and  Quinn  shows  that  the  racial  characters 
involved  differ  in  one  Mendelian  gene  (though  not  necessarily  one  in 
the  sex  chromosome).  However,  in  both  cases,  if  paternal  and 
maternal  elimination  are  equally  likely  in  both  combinations,  as  many 
gynandromorphs  showing  the  racial  character  of  only  one  type  are 
expected  as  those  mosaic  for  racial  characters  as  well  as  for  sex.  Such 
have  not  been  reported. 

(15)  (a)  In  moths  several  gynandromorphs  have  been  reported  that 
were  mosaics  for  paternal  and  maternal  characters  well  as  as  for  sex. 
Some  of  these,  starting  as  males,  can  be  explained  by  chromosomal 
eUmination. 


114  THE    ORIGIN   OF   GYNANDROMORPHS. 

(6)  In  Abraxas  a  factor  involved  is  known  to  be  sex-linked. 
Two  mosaics  between  A.  grossulariata  and  lacticolor  described  by 
Doncaster  can  be  accounted  for  by  chromosomal  elimination  in  one 
case  and  by  a  non-dis junctional  sperm  and  elimination  in  the  other. 

(c)  The  two  gynandromorphs  in  silkworms  described  by  Toyama 
can  be  explained,  genetically,  on  the  basis  of  two  nuclei  present  in  the 
eggs.     Doncaster  has  found  such  eggs  in  Abraxas. 

(d)  Whether  the  mosaics  in  the  gipsy  moth,  formed  by  racial  crosses, 
are  due  to  different  sex-factors  having  different  quantitative  value, 
as  maintained  by  Goldschmidt,  or  due  to  some  other  relations,  seems 
uncertain  from  the  evidence  so  far  published. 

(16)  In  reviewing  the  literature  it  is  pointed  out  that  in  the  Crus- 
tacea and  molluscs  there  are  several  cases  where  an  individual  is 
male  at  one  period  of  its  life  and  female  at  another,  just  as  some  plants 
pass  through  similar  stages.  In  such  cases  the  environment,  taken 
in  the  widest  sense,  may  suppress  one  sex  and  develop  the  other.  The 
influence  of  the  environment  is  clearly  shown  in  the  case  of  the  crabs 
infected  by  Sacculina,  where  the  secondary  sexual  characters  are  changed ; 
and  in  Crepidula,  where  proximity  to  another  individual  effects  a 
change  of  sex,  and  in  the  worm  Bonellia,  where  a  similar  change  is 
brought  about.  There  is  nothing  here  that  is  in  the  least  inimical  to 
the  view  that  in  other  cases,  and  even  in  these  same  groups,  there 
may  be  genetic  factors  that  determine  sex  under  ordinary  or  other 
circumstances.  The  bilateral  gynandromorph  of  the  crayfish  (p.  97) 
may  be  a  case  in  point. 

(17)  A  few  cases  of  bilateral  gynandromorphs  in  birds  have  been 
reported.  Their  occurrence  is  unexpected  because  of  the  known  effect 
of  the  ovary  in  suppressing  most  of  the  secondary  characters  of  the 
male.  It  is  suggested  that  in  some  species  of  birds,  particular  secondary 
sexual  differences  are  not  influenced  by  internal  secretions,  hence  a 
gynandromorph  condition  in  the  chromosomal  composition  might  show 
itself  in  plumage  characters.  It  is  also  suggested  that  if  a  bird  showed 
the  female  complex  in  one  region  and  a  male  complex  in  another  the 
amount  of  internal  secretion  that  might  inhibit  one  side  might  be  in- 
sufficient to  inhibit  the  other.  A  transient  or  an  abnormal  condition 
of  the  ovary  might  make  the  gynandromorph  differences  visible. 

(18)  In  man  and  in  other  mammals  a  number  of  cases  of  gynandro- 
morphs are  known,  some  of  them  at  least  well  authenticated.  Most 
of  the  cases  rest  on  the  condition  of  the  gonads  and  accessory  sexual 
organs.  Sex  mosaics  like  those  of  Drosophila  are  expected,  because 
the  mechanism  of  sex  determination  is  the  same.  On  the  other  hand, 
in  the  light  of  Lillie's  evidence  for  the  freemartin,  other  kinds  of  modifica- 
tions may  be  possible.  Even  in  cases  where  only  a  single  individual  is 
born  an  earlier  connection  with  an  absorbed  or  aborted  embryo  might 
be  responsible  for  an  abnormal  condition  of  the  sexual  organs. 


THE    ORIGIN    OF   GYNANDROMORPHS.  115 

POSTSCRIPT. 

Professor  F.  R.  Lillie  has  called  my  attention  to  two  important  papers  on 
freemartins.  It  appears  that  Tandler  and  Keller^  had  already  published,  in 
1911,  the  essential  facts  relating  to  the  vascular  connection  between  the 
embryos  in  utero,  leading  to  the  development  of  the  freemartin  out  of  the 
female  member  of  the  united  pair.  They  had  also  shown  that  the  embryos 
come  from  two  eggs,  Magnussen'^  in  1918  has  described  a  considerable 
number  of  cases  of  freemartins.  He  regards  both  individuals  as  having 
started  as  males,  and  compares  the  usual  rudimentary  condition  of  the  testes 
of  the  freemartin  with  that  of  a  cryptorchid  testis.  He  adduces  no  evidence 
of  importance  in  favor  of  his  view  that  the  twins  started  as  males,  while 
Lillie 's  evidence  is  convincing  in  support  of  the  view  that  the  freemartin 
started  as  a  female. 

The  most  important  facts  reported  by  Magnussen  are  those  relating  to  the 
histological  condition  of  the  testes  of  the  freemartin.  Well-developed  testes 
are  present  in  some  of  the  older  freemartins,  ranging  in  size  from  that  of  a 
hazel-nut  to  that  of  a  hen's  egg.  The  vasa  deferentia,  the  epididymus,  and 
notably  even  the  tubular  tissue  characteristic  of  the  testes  were  present,  but 
no  germ-cells  were  found.  Now  the  absence  of  germ-cells  from  the  tubular 
tissue  of  the  testes  of  the  adult  freemartin  may  be  accounted  for,  as  Magnussen 
does  account  for  it,  viz,  as  due  to  the  "retention"  of  the  testes  of  the  free- 
martin. This  condition  would  not,  however,  be  expected  to  hold  for  the 
embrj^onic  testes,  where  in  the  walls  of  the  testes  at  birth  one  would  expect 
to  find  the  germ-cells  present.  If  a  critical  examination  of  these  stages  shows 
that  germ-cells  fire  not  present  in  the  tubules  of  the  testes  of  the  freemartin, 
then  the  evidence  from  the  freemartin  shows  not  that  the  sex  of  the  female 
has  been  changed,  but  that  under  the  influence  of  the  blood  of  the  male  the 
accessory  organs,  as  well  as  the  secondary  sexual  organs  characteristic  of  the 
male,  have  developed  in  the  female;  while  at  the  same  time  her  own  female 
accessory  organs  have  correspondingly  failed  to  develop  fully.  This  state- 
ment implies  that  the  critical  evidence  for  sex  is  the  kind  of  germ-cell  produced, 
while  the  development  of  the  secondary  sexual  characters  and  of  the  accessory 
organs  of  reproduction  in  the  mammal  is  determined,  in  part  at  least,  by  the 
germ-cells.  It  will  be  recalled  that,  according  to  the  most  recent  work  in 
mammalian  embryology,  the  germ-cells  originate  in  or  from  the  region  of  the 
intestinal  tract,  far  removed  from  the  final  position  in  the  gonad  into  which 
they  find  their  way  by  migration.  If,  then,  it  prove  that  no  true  germ-cells 
are  found  in  the  testicular  tubules  of  the  freemartin,  the  presence  of  the 
"testes,"  including  even  the  epididymus,  and  tubules  demonstrates  only  how  far 
the  origin  of  these  parts  is  dependent  on  something  in  the  male ;  but  whether 
this  something  comes  from  the  germ-cells  of  the  male  (directly  or  indirectly) 
or  is  a  consequence  of  the  genetic  composition  of  the  male  is  not  shown. 

July  17,  1919, 

1  Tandler  und  Keller,  1911.  Ueber  das  Verhalten  des  Chorions  bei  verschieden-geschlocht- 
licher  ZwillinRSgravitat  des  Rindes,  uhd  ueber  die  MorpholoRie  des  Genitales  der  weiblichen 
Tiere,  welche  einer  solchen  Gravitat  enstammen.  Deutsche  tieraerzliche  Wochenschrift. 
(No.  10.) 

^  Magnussen,  H.,  1918.  Geschlechtslose  Zwillinge.  Eine  gewohnlich  Form  von  Herma- 
phroditismus  beim  Rinde.     Archiv.  f.  Anat.  u.  Physiol.  Anat.  Abt. 


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St.  George,  La  Vallette.     1895.     Zwitterbildung  beim  kleinen  Wassermolch  {Triton 

Usniatus).     Arch.  f.  mikr.  Anat.,  XLV. 
Standfuss,  M.     1896.     Handbuch  der  Palaarktischen  Gross-Schmetterlinge.     Jena. 
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Folge  der  innersekretorischen  Funktion  der  Keimdriisen.     Zentralbl.  f.  Physiol., 
XXIV. 

.     1912.     WillkiirUche  Umwandlung  von  Saugetier.     Maunehen  in  Tiere  mit  aus- 

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Ges.  Phys.,  144. 
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Stevens,  N.  M.     1905.     Studies  in  spermatogenesis,  with  especial  reference  to  the  "ac- 
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.     1908.     A  study  of  the  germ-cells  of  certain  Diptera.     Jour.  Exp.  Zool.,  V. 

.     1909.     An  unpaired  chromosome  in  the  aphids.     Jour.  Exp.  Zool.,  VI. 

.     1911.     Heterochromosomes  in  the  guinea-pig.     Biol.  Bull.,  XXI. 

Strong,  R.  M.     1912.     Results  of  hybridizing  ring-doves,  including  sex-linked  inheritance. 

Biol.  BuU.,  XXIII. 
Stout,  A.  B.     1915.     The  establishment  of  varieties  in  Coleus  by  the  selection  of  somatic 

variations.     Carnegie  Inst.  Wash.,  Pub.  No.  218. 
Sturtevant,  a.  H.     1915.     Experiments  on  sex  recognition  and  the  problem  of  sexual 

selection  in  Drosophila.     Journ.  Animal  Behav.,  V. 
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'<  ii 


II. 


THE  SECOND-CHROMOSOME  GROUP  OF  MUTANT 

CHARACTERS. 

By  C.  B.  Bridges  and  T.  H.  Morgan. 


With  seven  plates  and  seventeen  text-figures. 


123 


J. 


THE  SECOND-CHROMOSOME  GROUP  OF  MUTANT 

CHARACTERS. 


By  C.  B,  Bridges  and  T.  H.  Morgan. 


INTRODUCTION. 

This  paper  deals  with  39  mutant  races  whose  genes  He  in  the  "second 
chromosome.' '  This  number  includes  all  of  those  previously  described, 
and  gives  a  complete  account  of  all  the  second-chromosome  mutants 
found  before  1916.  The  latter  have  been  for  the  most  part  used  or 
mentioned  in  previous  papers  by  ourselves  and  others.  It  has  been 
our  rule  never  to  hold  back  any  useful  mutant  type  until  it  had  been 
recorded  by  its  discoverers,  and  in  consequence  a  number  of  the  char- 
acters here  described  for  the  first  time  have  already  been  used  widely. 
This  applies  equally  to  the  third-chromosome  mutants,  an  account 
of  which  we  hope  to  publish  soon. 

In  addition  to  the  39  mutant  types  here  described  there  remain 
about  35  others  discovered  since  1915  which  are  still  to  be  described. 
In  making  our  selection  for  the  present  publication  we  have  included 
those  which  are  most  essential  for  future  work  both  in  localization  of 
genes  and  in  special  experiments.  For  example,  star  eye,  because  of 
the  location  of  the  gene  at  the  extreme  'left'  end  of  the  chromosome,  of 
its  dominance,  and  of  its  other  excellent  characteristics,  is  now  the  most 
generally  useful  second-chromosome  mutant.  Again,  purple  eye- 
color  is  the  only  workable  eye-color  in  this  chromosome.  It  has  been 
involved  in  the  localization  of  many  of  the  genes  in  the  chromosome. 
Its  position  is  at  the  center  of  the  chromosome,  which  center  shows 
certain  important  peculiarities.  Furthermore,  its  location  near  black 
gives  a  working  distance  suitable  for  analyzing  linkage  and  coincidence 
characteristics;  the  distance  between  purple  and  black  is  short  enough 
to  exclude  double  crossing-over  and  long  enough  to  exclude  the  large 
and  uncertain  probable  error  incident  to  small  percentages  of  crossing- 
over.  A  third  important  mutant  type,  speck,  whose  gene  is  located 
near  the  right  end  of  the  chromosome,  is  used  as  the  basis  of  reference 
of  the  genes  of  that  end  of  the  chromosome.  Finally,  curved  is, 
in  addition  to  its  excellent  viability,  ease  of  identification,  and  other 
useful  features,  very  valuable  from  its  position  at  the  right  of  the  cen- 
tral group  of  the  most  useful  and  best  located  genes. 

The  mutants  have  been  discussed  in  order  of  their  discover}-,  since 
this  method  involves  least  use  of  material  requiring  special  explana- 

125 


126 


THE    SECOND-CHROMOSOME    GROUP 


tion,  and  the  earlier  experiments  were  relatively  simple.  In  the  case 
of  several  of  the  mutants  found  very  early,  Uttle  more  than  a  review 
of  the  extensive  work  abeady  published  has  been  given. 

A  chronologically  arranged  list  of  all  these  mutants,  together  with 
a  sumniiiry  of  main  points  with  respect  to  their  origin,  locus,  etc.,  is 
given  in  table  1. 

Ta  ule  1 . — Chronologically  arranged  list  of  1 1 -chromosome  mutant  genes  treated  in  this  paper. 


Mutant 
gene. 


Speck. 


Olive 

Truncate. 
Black 


DalliK)n . 
Vealigial . 


Lethal  T' . 
Blistered . 


Jaunty . 
Curved. 


Purple . 
Strap .  . 
Arc . . . . 


Gap 

Antlered . 

Dacbs. . . 


Streak . 


Comma*.  . 
Morula. ... 
Apterous*.  , 

Cill 

Ciir 

Cream  II*. 
Patched*.  . 

Trefoil*... 


Cream  6*. . 

Pinkish*  . 
Plexus    ... 
Limited.  .  . 
Confluent*. 


Fringed*. 
SUr 


Nick 

Dachs-lcthal 
Squat* 


Lethal  Ila.. 
Telescope . . . 


Modifiers. 


Dachsoid 


Affects  mainly- 


Fig. 


Axil  of  wing. 


Body-color. . 
Wing-length. 
Bodv-color. . 


Wing,  venation. 
Wing,  balancer. 


Life 

Venation. 


Wing  curvature. 
Do. 


Eye-color 

Wing 

Wing  curvature. 


Venation . 

Wing 

)  Venation 
I  Legs 


Thorax  pattern. 


Thorax  marks.  . 

Eye-facets 

Wing,  balances. 
II  crossing-over. 
Do. 

Eye-color 

Abdomen 


Thorax  pattern . 
Eye-color 


Do. 
Venation. 
Abdomen. 
Venation. 


Wing 

Eye-faceta . 


Wing. 
Life.. 
Wing, 


Life 

Abdomen,  wing . 


Dichsete . 


■ 


Venation . 


PI   5,  figs.  I 
and  4.  text- 
fig.  73. 

PI.  .'■>,  fig.  1., 

PI.  6 

PI.  5,  fig.  2.. 

PI.  7.  fig.  1.. 
PI.  7.  fig.  2. . 


Text-fig.  74 

PI.  7,  fig.  3. 
Text-fig.  75 


PI.  5,  fig.  8. 

PI.  8 

PI.  7,  fig.  4. 


Text-fig.  76 . 

PI.  9 

PI.  10 

Figs.  la-Id.. 

/PI.  5,  fig.  5.. 
\P1.  10,  fig.  2, 


Text-fig.  79 
PI.  10,  fig.  3, 
PI.  7,  fig.  5. 


PI.  5,  fig.  10 
PI.  11 

J  PI.  5,  fig.  6.. 

\P1.  8.  fig.  1.. 

PI.  5,  fig.  11 . 

PI.  5,  fig.  12. 
Text-fig.  80. 
Text-fig.  81 


Text-fig.  82 
Text-fig.  83 

Text-fig.  84 


Text-fig.  85 


PI.  7.  fig.  6. 


Text-fig.  86 


Sym- 
bol. 


Locus. 


sp 

ol 

r 

b 

ha 
Vg 


It 

} 
c 


Pr 

Vgl 

a 
gp 

tgO 
d 


St 


mr 

CilJ 
Clir 
crii 


I" 

crb 

Px 
C/ 


fr 

S' 

tgn 
dl 
Sa 

Ina 
tt 


S'  +     Primary  base 


105.1 

106.1= 
28.0 
46.5 

105.5 
65.0 


103      = 

46.7 
73.5 


52.7 
65.0 
98.4 


c-l-31.6 

sp+  1.    = 
S'-t-28.0 


65.0 
29.0 

15.4 


106.3 
48.5 


50 


22.5 

100.    -I- 
96.2 
106.3 


98.0  = 
0.0 

65.0 
29.0 
35.5 


62 
66, 


«j7+0.4 
pr+l2.3 


r=fcl5 
sp—  2 

6+0.2 
pr+20.8 


b+  6.2 
rff±  0.0 
sp  -6.7 


tg=>=  0.0 
6-18.5 

d-13.6 


Sq  =t  15 
a+  7.9 

S'-t-48.5± 
6-? 

pi—? 


Date 
found. 


64-60     : 
Sp-  8.9 
mT+7 


6+51.5 
St-15.4 

va±  0.0 
d=t  0.0 
6-11.0 

c-10.8 


sp- 


1910 
Mar.  — 

May  — 
Aug.  — 
Oct.  — 

Nov.  — 
Dec.  — 

1911 
Feb.  — 
Nov.  16 

Dec.  11 
Dec.  24 

1912 
Feb.  20 
Apr.  — 
May  24 

July  10 
Sept.  — 
Oct.  — 
Nov.  22 

Nov.  27 

1913 
Feb.  5 
Mar.  8 
Aug.  — 
Sept.  — 
Sept.  — 
Sept.  15 
Nov.  25 

Nov.  — 

1914 
Mar.  10 

July  27 
Aug.  20 
Sept.  13 
Sept.  23 

1915 
Jan.  20 
Feb.  12 

May  7 
Oct.  6 
Nov.  29 

Dec.  2 
Dec.  27 


1916 
Aug.  13 

1917 
Feb.     9 


Arose  from — 


Wild  stock . 


Do. 

Beaded  stock. . 
Miniature    ex- 
periment. 
Truncate  stock 
Do. 


Do. 

Rudimentary 

stock. 

Do. 

Do. 


Tg  stock 

Do. 
Black-palpi 
stock. 

bXa 

Vg  experiment 


Sable     experi- 
ment. 

'Lop'   stock. . 


dXpink 

peach  Xwild  .. 
wm  stock.  ... 
"  Nova  Scotia' 

Do. 
Lethal  2  stock 


Culture 
No. 


Non-disjunc- 
tion. 

Eosin  6  stock . 

Spread  stock. 

mr  stock 

Non-disjunc- 
tion. 

Jaunty  I 

Non-disjunc- 
tion. 

Lethal  2 

S'Xd 

Non-disjunc- 
tion. 

S'b  c  stock .  .  . 

'Crooked'     ex- 
periment. 


D  stock 


Eosin  X  'seple' 


A  23 

A  34 
A  43 


A  66 
BSO' 
B42 


C146 
C149 


II  9 
M20 


M68 


82 


557 
511 
550 


1,042 
1,347 

2,012 
2,217 
2,480 

2,675 
2,735 


2,671 


*Th«  mutations  marked  with  the  asterisk  (*)  are  no  longer  on  hand,  having  been  lost  or  discarded. 


OF   MUTANT   CHARACTERS. 


127 


Special  attention  has  been  given  in  the  treat- 
ment of  the  data  to  bring  out  the  genetic  methods 
employed,  and  to  trace  the  development  of  such 
methods.  The  part  each  mutant  has  played  in 
this  development  of  methods  and  principles  lias 
been  given  fully,  often  at  the  expense  of  repeti- 
tion. An  effort  has  been  made  to  evaluate  each 
mutant  with  respect  to  its  usefulness  as  a  working 
tool.  Some  are  practically  useless,  while  certain 
others,  from  the  possession  of  excellent  charac- 
teristics or  favorable  location  in  the  chromosome, 
etc.,  must  be  considered  in  every  carefully  planned 
experiment.  By  such  methods  of  presentation  it  is 
hoped  to  make  available  not  simply  a  body  of  data 
but  also  a  working  familiarity  with  the  material. 

From  the  various  published  and  hitherto  un- 
published materials  on  crossing-over  in  the  second- 
chromosome  a  summary  is  given  of  total  data 
available  on  amount  of  crossing-over  between  va- 
rious loci  (table  140).  The  cross-over  values  cal- 
culated from  these  data  are  still  further  summar- 
ized and  presented  in  graphic  form  in  the  map  of 
the  second  chromosome  which  appears  as  fig.  72. 

In  the  construction  of  this  map  it  was  necessary 
to  correct  some  of  these  values  by  aid  of  informa- 
tion gained  from  a  study  of  the  amount  of  double 
crossing-over  and  coincidence  in  the  various  re- 
gions of  the  second  chromosome.  Details  of  how 
this  was  done  will  be  found  in  the  last  section, 
which  deals  with  the  construction  and  use  of 
this  map.  The  coincidences,  and  consequently 
the  corrections,  are  at  present  only  quite  rough 
approximations,  and  the  same  is  true  of  the  meth- 
ods of  weighting  employed  in  that  section.  It 
should  be  borne  in  mind  that  the  map  is  a  com- 
posite picture  in  which  differences  in  the  data  from 
different  sources  are  no  longer  apparent.  Ref- 
erence to  these  separate  data  will  show,  however, 
a  very  surprising  uniformity,  especially  in  view 
of  the  many  conditions  now  known  to  be  able  to 
cause  the  amount  of  crossing-over  to  vary. 

A  glance  at  the  map  shows  at  the  right  end  (bot- 
tom) an  unusually  dense  cluster  of  genes.     WTien 

Text-figure  72. — Map  of  the  second  chromosome,  giving  the 
locations  with  reference  to  star,  and  the  symbols  of  the 
mutants  whose  loci  are  known. 


0  0--  Stiir  (  S  1 


15   V    -  SU-eaJc(3;4) 


2.5--  Creamb(Crbt 


Ufl.O 


3S5--  S<j<iat(Sj) 


4o  5 
46  T 
■+8.5 


Aptci-6us(a.p> 
Trefoadjl 

--  Piu-plc(p    1 


GSO 
66  5 


105.1^ 
105.S- 
106  I  ? 

106  3 


Ti-unca»*(T> 

L)aclu(dl, 

dacha-IeUuil(di) 


2  5--Lethal  tlaC  1, 


.  .Vestigial  (vrfi,9trap(vg*|. 
--Tclescopc^tsl  * 


73  5-  -  Curved  (c) 


96  2  -  -  Plexus  (  Pj^  I 

98  o..  Frmged  UV' 
98.VT.\rC(ln 


Blistered  (bg) 

/Speck  (Sp) 
BaIlooii(ba.l 
"  Oliw  ( i>i ) 
'Morula  (nij-l. 
lunitBd  T 

FlO.  72. 


128  THE    SECOND-CHROMOSOME    GROUP 

we  come  to  add  to  the  map  the  loci  of  the  genes  as  yet  unpublished, 
another  such  cluster  will  appear  at  the  left  end  of  the  chromosome 
also.  These  clusters  at  the  ends  may  be  looked  upon,  not  as  due  to 
the  genes  being  here  actually  nearer  together,  but  to  the  probability 
that  at  the  ends  crossing-over  is  relatively  less  frequent  than  in  the 
middle  part  of  the  chromosomes.  The  bearing  of  the  information  as 
to  the  relative  frequency  of  double  crossing-over  on  the  conclusion  just 
stated  is  discussed  in  the  section  on  "Purple." 

To  the  reader  who  is  not  especially  concerned  with  the  localization 
of  the  genes,  we  should  like  to  call  attention  to  other  subjects  of  very 
general  interest,  such  as  the  discussion  of  modifiers  in  the  sections 
on  purple,  the  creams,  star,  and  the  second-chromosome  modifier  of  the 
third-chromosome  character,  dichaete.  Another  topic  of  general  inter- 
est is  that  of  autosomal  and  balanced  lethals  discussed  in  the  sections 
on  truncate,  streak,  confluent,  star,  dachs-lethal,  and  lethal  Ila.  A 
third  topic  of  interest  is  that  of  variations  in  the  amount  of  crossing- 
over  due  to  specific  genes  and  to  such  factors  as  age  and  temperature 
that  are  discussed  in  the  sections  on  purple,  dachs-lethal,  and  in  the 
summary  dealing  with  the  cross-over  variations  Cm,  and  Cur- 

SPECK  (5p). 

(Text-figures  73  a  and  b,  75  b,  and  plate  5,  figures  1  and  4) 

ORIGIN  AND  STOCK  OF  SPECK. 

In  the  course  of  the  early  work  upon  Drosophila  in  the  Columbia  Zoo- 
logical Laboratory  a  selection  experiment  was  carried  out  by  Morgan 
upon  a  race  of  wild  flies  that  had  showed  variation  in  the  extent  and  dark- 
ness of  the  shield  or  trident  pattern  upon  the  thorax.  In  the  fourth  gen- 
eration of  selection  for  a  race  "without"  such  a  trident,  there  appeared 
(March  1910)  a  few  individuals  with  a  tiny  black  speck  (plate  5,  fig.  4) 
at  the  juncture  of  each  wing  wdth  the  thorax  (Morgan,  1910).  At  first 
the  breeding  results  obtained  with  this  character  were  irregular  (Mor- 
gan, 1910).  Some  of  this  irregularity  may  have  been  due  to  non-virgin 
females  (24-hour  females  were  used)  and  to  the  practice  of  using  mass 
cultures,  though  probably  more  was  due  to  difficulty  of  classification 
before  familiarity  with  the  characteristics  of  the  mutation  had  been 
acquired. 

A  stock  pure  for  the  character  was  obtained,  but  was  set  aside  in 
order  that  more  time  might  be  given  to  the  study  of  the  sex-linked 
eye-color  white  which  had  appeared  in  April  1910.  About  a  year 
after  this  (May  1911)  it  was  found  that  a  stock  of  flies  with  a  dark 
body-color  called  "olive"  was  pure  for  a  character  which  was  taken  to  be 
the  same  as  speck  (text-figs.  73  a  and  73  b).  Accordingly,  the  first  and 
simpler  speck  stock  was  discarded  and  the  olive  stock  was  retained. 
There  is  some  uncertainty  with  regard  to  this  "olive"  stock,  but  it  seems 


PLATE  5 


] .    Speck  olive 


2.    Hlaek 


'<  w:.i,  " 


3.    "With 


l';/'!j^ 


-1  iff- 


4 


>->. 


7.     \\iM-t>i.e 


V.    Eosiii  (j 


^. 


■■> 


10.    Creatn    II.    ^ 


II.    C  ii-.iin   h.    ^"Z 


i:.    Pinkish.   rT 


4.   Speck  "without" 


M-   Waulack    Pinx 


SECOND  CHROMOSOME    MUTANTS   OF   DROSOPHILA 


OF    MUTANT    CHARACTERS. 


129 


probable  that  it  was  derived  from  a  stock  different  from  the  line  of 
trident-pattern  selection  which  gave  rise  to  the  "with"  and  to  the 
"without"  stocks.  The  early  selection  experiments  appear  to  have 
resulted  in  four  stocks:  (1)  "without"  trident  pattern,  (2)  "without" 
pure  for  the  original  speck,  (3)  "  with  "  trident  pattern,  and  (4)  "olive " 
stock.  The  stocks  of  "with"  and  of  "olive"  differed  in  the  character  of 
the  trident  pattern  in  that  the  "with"  is  a  sharp  darkening  of  the  trident 
pattern,  while  "olive"  is  a  more  diffused  darkening.  Subsequent 
analysis  of  the  genetic  behavior  of  these  stocks  showed  that  the  "with" 
was  a  simple  third-chromosome  semi-dominant,  while  the  "olive"  was 
a  trimutant  stock  homozygous  for  olive  II,  olive  III,  which  is  a  third- 
chromosome  recessive  mutant  not  distinguished  in  appearance  from 
olive  II,  and  "speck,"  which  is  a  second-chromosome  recessive.  An  old 
figure  (plate  5,  fig.  4)  bears  out  our  recollection  that  the  original  speck 
was  due  to  a  tiny  brush  of  hairs  on  the  side  of  the  thorax  above  the 
wing  juncture.  The  new  speck  is  a  black  pigment  spot  in  the  axil  of 
the  wing.  The  original  speck  seems  not  to  have  been  dependable  in  its 
behavior,  while  the  new  speck  has  behaved  with  perfect  regularity  in 
inheritance.  Thus,  both  the  nature  of  the  characters  themselves  and 
the  nature  of  the  trident  mutants  associated  with  the  two  "specks"  lead 
to  the  conclusion  that  they  were  not  the  same  mutants,  as  had  been  too 
hastily  assumed.  The  new  speck  from  olive  stock  will  be  referred  to 
hereafter  as  speck,  while  the  original  speck  will  be  called  the  old  speck. 

DESCRIPTION  OF  SPECK. 

The  character  speck,  as  seen  with  the  magnification  with  which  we 
ordinarily  work  (about  15  diameters),  is  due  to  the  presence  of  a  minute 
but  intensely  black  round  speck  in  the  axil  of  each  wing.  The  speck 
is  clearly  seen  from  above  (fig.  73  a)  or  from  a  little  below  the  side 
(figs.  73  b,  75).     Under  the  microscope  the  speck  is  seen  to  consist  of  a 


Text-figure  73. — Speck:  a,  side  view;  b,  from  above. 


130 


THE    SECOND-CHROMOSOME    GROUP 


hea,\y  deposit  of  pigment  in  the  lips  of  a  spiracle  which  is  situated 
a  little  behind  and  below  the  juncture  of  the  base  of  the  wing  with 
the  thorax  (fig.  73  6).  There  is  also  present  upon  the  side  of  the 
sciitellum  and  of  the  thorax  both  above  and  below  the  wing  an  added 
faint  tinge  of  pigment  or  areola  which  seems  to  persist  after  olive  has 
been  eliminated  from  speck.  However,  speck  is  rarely  seen  without 
a  decided  olive  color,  because  the  gene  for  olive  is  very  closely  linked 
to  that  for  speck.  Since  there  is  always  the  chance  of  crossing-over 
between  speck  and  olive,  and  since  certain  other  genes  give  roughly 
similar  pigmentation,  it  is  well  to  disregard  this  pigmentation  and 
classify  by  means  of  the  speck  alone,  which  is  in  itself  a  sufficient 
index  of  the  speck  gene. 

INHERITANCE  AND  CHROMOSOME  OF  SPECK. 

During  the  fall  and  winter  of  1912  considerable  breeding-work  with 
speck  was  carried  out.  The  results  of  these  experiments,  particu- 
larly of  the  F2  from  the  crosses  of  speck  olive  by  black,  contained  the 
answer  to  the  questions  as  to  which  chromosome  carried  the  genes  for 
speck  and  for  olive,  but  the  records  were  not  carefully  examined  until 
May  1913.  Meanwhile,  Sturtevant  had  begun  to  work  with  speck 
(December  1912)  and  had  shown  that  it  was  a  complete  and  invari- 
able recessive  and  behaved  with  regularity  in  inheritance. 

Table  2. — Pi,  speck  olive  9   X  wild  cT;  Fi  wild- 
type   9+^1  wild-type  cf. 


1912. 
Dec.  — . 

Wild-type. 

Speck. 

Olive. 

Speck  olive. 

9 

d' 

9 

d^ 

9 

d' 

9 

d^ 

la 

16 

2a 

26 

3a 

36 

4a 

46 

5a 

56 

Total.  . 

41 
63 
44 
62 
38 
92 
58 
13 
68 
5 

49 
73 
23 
38 
46 
117 
75 
11 
74 
5 

2 

5 

1 
5 
1 
8 
5 
1 

1 
1 

2 
1 
4 
4 
2 

"2 
3 

37 
20 
32 
38 
11 
18 

7 
10 
18 

8 

20 
7 
39 
25 
17 
11 
2 

11 

15 

6 

25 
32 
21 
35 
32 
49 
31 

8 
28 

6 

25 
27 
23 
17 
22 
33 
16 

4 
27 

5 

484 

511 

28 

20 

199 

153 

267 

199 

By  means  of  the  2: 1 :  1 : 0  ratio  in  the  F2  of  the  cross  of  curved  to 
speck  he  showed  that  speck  was  a  member  of  the  second-chromosome 
group.     (Jan.  13,  1913). 

In  the  crosses  carried  out  by  Miss  Wallace,  speck  was  found  to  be 
readily  classified  and  fully  viable.  Speck  olive  females  were  crossed 
to  wild  males  and  10  F2  pair  cultures  raised  (table  2).  The  reciprocal 
cross  (speck  d"  X  wild  9 )  was  also  made  to  the  extent  of  5  F2  cultures 


OF   MUTANT    CHARACTERS. 


131 


(table  3).  These  two  crosses  gave  identical  results  as  to  the  distribu- 
tion of  both  characters  and  sex,  which  proved  that  no  sex-linkage  was 
involved.     They  may  therefore  be  combined  and  considered  together. 

The  total  number  of  flies  produced  was  2,857,  of  which  772  or  27  per 
cent  were  speck,  which  is  in  agreement  with  the  fact  that  speck  is  a 
simple  autosomal  recessive. 

Table  3. — Pi  speck  olive  cT  X  wild  9 ;  Fi  vrild- 
type   9    -h  Fi  wild-type  cT. 


1912. 
Dec.  — . 

Wild-type. 

Speck. 

Olive. 

Speck  olive. 

9 

d" 

9 

cf 

9 

<f 

9 

& 

a  1 

bl 

b2 

d2 

d  1 

Total .  . 

Totals  of 
tables  2 
and  3 .  . . 

46 
44 
55 
31 
107 

67 
37 
45 
25 
104 

4 

1 
5 
1 

i 

1 

3 
2 

56 
35 

4 
11 

5 

29 
27 

6 
4 

24 
29 
24 

8 
42 

30 
19 
17 
11 
36 

283 

278 

11 

7 

111 

66 

127 

113 

1,556 

66 

529 

706 

The  inheritance  of  ''olive"  was  also  followed,  but  since  this  will  be 
treated  in  the  following  section  it  need  only  be  stated  here  that  the 
ratio  of  wild-type  to  olive  was  9 :  7,  which  indicates  two  recessive  body- 
color  genes  giving  similar  somatic  effects  and  assorting  independently 
of  one  another.  One  of  these  is  olive  III,  (Ill-chromosome  recessive) 
and  the  other,  olive  proper  (II  chromosome,  closely  linked  to  speck) . 

Speck  olive  males  were  crossed  to  black  females,  and  5  F2  pair  cul- 
tures (table  4)  and  5  more  from  the  reciprocal  (table  5)  were  raised. 
The  significant  fact  observed  in  these  crosses  was  that  none  of  the 
blacks  were  speck,  which  means  that  speck  has  its  locus  in  the  second 
chromosome.  The  combined  data  (disregarding  olive)  give  1,098 
wild-type,  490  black,  466  speck,  0  black  speck,  which  is  an  approxi- 
mation to  the  2:1:1:0  ratio  expected  from  such  a  cross. 

Table  4. — Pi,  speck  olive  cf  X  black  9 ;  Fi  ivild-type  9   -\-  Fi  wild-type  (f 


1912. 
Dec.  — . 

Wild- 

type. 

Speck. 

Olive. 

Speck 

olive. 

Black. 

Black  speck. 

9 

d' 

9 

& 

9 

d^ 

9 

cf 

9 

0^ 

9 

0^ 

a  1 

a2 

bl 

b2 

c  1 

Total. .  . 

34 

10 

8 

5 

45 

36 
17 
10 
5 
43 

3 

2 

1 

42 
11 
14 
47 
20 

14 
12 
11 
32 
10 

29 

8 

7 

34 

30 

25 
12 
10 
22 
14 

34 
12 
17 
18 
26 

38 

9 

10 

25 

8 

0 
0 
0 
0 
0 

0 
0 
0 
0 
0 

1 

102 

111 

6 

1 

134 

79 

108 

83 

107 

90 

0 

0 

132  THE   SECOND-CHROMOSOME    GROUP 

Table  5.— Pi,  speck  olive  9   X  black  d";  Fi  wild-type  9  +  Fi  mid-type  cf . 


1912. 
Dec.  — . 

Wild-type. 

Speck. 

Olive. 

Speck  olive. 

Black. 

Black  speck. 

9 

cT 

9 

c? 

9 

d^ 

9 

d" 

9 

d^ 

9 

& 

ib 

ii  a 

lib 

iv  fc 

v6 

Total. .  . 

Totals     of 
tables     4 
and  5 

37 
27 
54 
57 
28 

35 
26 
43 
57 
42 

1 

1 

1 
3 
1 
5 

31 
63 
40 
17 
13 

31 

40 

13 

9 

9 

35 
32 
16 
29 

18 

27 
26 
29 
24 
20 

21 
44 
31 
38 
14 

25 
26 
33 
39 
22 

0 
0 
0 
0 
0 

I 

0 
0 
0 

203 

203 

1 

11 

164 

102 

130 

126 

148 

145 

0 

0 

619 

19 

479 

447 

590 

0 

There  was  confusion  in  the  classification  of  the  oHve  in  these  crosses 
of  olive  to  black,  since  flies  heterozygous  for  black  are  intermediate 
and  were  often  classified  as  olive. 

LOCUS  OF  SPECK. 

At  this  time  it  was  known  that  the  genes  black,  purple,  vestigial,  and 
curved  were  in  the  second  chromosome  alined  in  the  order  named 
(Morgan  and  Lynch,  1912;  Morgan,  1912;  Bridges  and  Sturtevant, 
1914).  A  position  for  speck  still  further  to  the  right  was  indicated 
by  the  cross-over  values  of  table  6.     Since  this  eariier  work  was 

Table  6. — Data  upon  the  crossing  over  of  speck  with  other  second-chromosome 
genes,  summarized  from  Sturtevant,  1915. 


Loci. 

Total. 

Cross-overs. 

Per  cent  of 
cross-overs. 

Black  speck 

Vestigial  speck.  .  . 
Curved  speck .... 

223 
1,446 
1,007 

110 
520 
262 

49.3 
36.0 
26.0 

Table  7. — Pi,  purple  curved  speck  cf   X  wild  9 ;  B.  C,  Pi  mid-type  9    X 

purple  curved  speck  c^  from  stock. 


1914. 
Aug.  24. 

Pr     c     8p 

Pr 

Pr     c 

Sp 

Pr 

Sp 

C     Sp 

c 

Purple 
curved 
speck. 

Wild- 
type. 

Purple. 

Curved 
speck. 

Purple 
curved. 

Speck. 

Purple 
speck. 

Curved. 

452 

99 
69 
24 
51 

97 
74 
53 
56 

25 
15 
14 
17 

28 
24 
20 
20 

54 
26 
23 
26 

47 
27 
22 
22 

4 

1 
2 
3 

4 

481 

507 

4 
1 

508 

Total 

243 

280 

71 

92 

129 

118 

9 

10 

if 


m 


OF    MUTANT    CHARACTERS. 


133 


Table  8. — A  summary  of  the  cross-over  data  involving  speck. 


Loci. 


Star  speck  .  .  . 


Streak  speck . 
Dachs  speck. , 

Black  speck . 


Purple  speck . 


Vestigial  speck 


Curved  speck.. 


Plexus  speck  . . 

Arc  speck 

Blistered  speck 
Speck  balloon  . 


Total. 


369 


6,766 


7,135 


462 
462 

223 

462 


685 


462 

952 

2,625 

6,766 

259 

565 
356 


11,985 


1,446 
146 

462 


2,054 


1,007 
223 

462 
952 


6,766 

632 


10,042 


327 

2,625 

36 
462 


Cross- 
overs. 


185 


3,264 


3,449 


242 
231 

110 

216 


326 


218 

410 

1,116 

3,130 

95 

279 
176 


5,474 


520 
40 

178 


738 


262 
71 

150 
266 

2,062 

226 


3,037 


29 
156 

3 
2 


Per 

cent. 


50.1 


48.3 


48.4 


52.3 
50.0 

49.3 

46.8 


47.6 


47.2 
43.1 
44.4 

46.3 

36.7 

49.4 
49.4 


45.7 


36.0 

27.4 

38.5 


35.9 


26.0 
31.8 

32.5 
27.9 


35.7 


30.5 


8.9 

5.9 

8.3 
0.4 


Date. 


1915 
June  28 


July  11 


1914 
May  — 

May  — 
1913 

Oct.  16 
1914 

May  — 


May  — 
Aug.  24 
Oct.  24 

1915 
July  11 

1916 
Feb.    7 

Feb.  8 
Feb.  29 


1913 
Mar.  14 
Oct. — 

1914 
May  — 


1913 
Mar.  10 
Oct.    16 

1914 
May  — 
Aug.  24 

1915 
July  11 

1916 
Feb.    8 


Feb.  29 

1914 
Oct.  24 

Feb.  27 
May  — 


By  — 


Bridges . . . 
Do. 

Muller 

Do. 

Sturtevant 

Muller 

Muller 

Bridges . . . 
Do. 

Do. 

Do. 

Do. 
Do. 


Sturt«vant. 
Do. 


Muller. 


Sturtevant . 
Do. 


Muller . . 
Bridges . 

Do. 

Do. 

Do. 

Do. 

Do. 
Muller. . 


Reference. 


'^'   — -  B.C.;  180G-'08. 


S'; 


S' 


Pr  C  Sp 


B.  C.;l8t.s;  ia36-'94. 


Am.  Nat.  '16,  p.  422. 
Do. 

Zeit.  f.  i.  A.  u.  Ver.  '15,  p.  245. 

.\m.  Nat.  '16,  p.  422. 

Do. 
»j»;  Pr  c  Sp  B.C. ;  452-508. 
a;  PrOSp  balanced  B.C. ;  637-686. 


S';^ 


B.C.;l8t8;1836-'94. 


Pt  c  Sp 

Pr fp 

hia!    I  fi!  3168.. 

hia:  PrCSpFi;  3203-8. 
hi  a;  Pr  Px  «p  Fi:  3535. . 


Zeit.  (.  i.  A.  u.  Ver.  '15.  p.  245. 
Zeit.  f.  i.  A.  u.  Ver.  '15,  p.  287. 

Am.  Nat..  '16.  p.  422. 


Zeit.  f.  i.  A.  u.  Ver.  '15.  p.  245. 
Zeit.  f.  i.  A.  u.  Ver.  '15.  p.  247. 

Am.  Nat.,  '16.  p.  422. 
Sp!  p,  c  Sp  B.C. ;  452-508. 


S': 


B.C.  firsts;  1836-'94. 


Pt  c  Sp 
111  a:  Pt  c  8p  Ft;  3203-8. 


hia-'  Pt  Pi  «i>  ^i-"  3535. 


a;  Pr  a  Sp  balanced  B.C. ;  637-686. 
bt:  -^—    B.C.;  72.... 

Sp 

Am.  Nat..  '16.  p.  422. 


134  THE   SECOND-CHROMOSOME    GROUP 

finished,  very  large  amounts  of  additional  accurate  data  have  been 
collected  upon  the  cross-over  relations  of  speck  with  other  second- 
chromosome  genes.  These  data  appear  in  the  tables  of  the  sections 
following  this  (see  especially  star). 

Only  one  of  these  later  experiments  had  as  the  main  object  the  more 
exact  determination  of  the  locus  of  speck.  This  experiment  (table  7) 
was  a  triple  back-cross  for  the  three  loci — purple,  curved,  and  speck — 
and  gave  a  curved  speck  cross-over  value  of  27.9  per  cent  on  the  basis 
of  the  952  flies,  of  which  266  were  cross-overs  between  curved  and  speck. 
The  base  of  reference  in  the  determination  and  mapping  of  the  locus 
of  speck  is  curved,  which  is  the  nearest  locus  accurately  mapped  in 
relation  to  black,  the  primary  base  of  the  entire  second  chromosome. 

For  the  sake  of  convenience  a  sunamary  of  all  the  cross-over  data  in 
which  speck  is  one  of  the  loci  involved  is  given  in  table  8.  In  calcu- 
lating the  locus  of  any  mutant  one  must  consider  not  only  this  direct- 
linkage  data,  but  also  the  whole  mass  of  data  on  the  other  loci  of  the 
same  chromosome,  and  especially  the  information  upon  the  amount 
of  double  crossing-over  and  coincidence  in  the  various  regions.  By 
this  method  speck  has  been  mapped  at  a  locus  31.6  units  to  the  right  of 
curved,  which  is  its  immediate  base  of  reference,  or,  referring  back  to 
star  as  the  zero-point,  speck  is  at  105.1. 

VALUATION  OF  SPECK. 

Speck  is  at  present  one  of  the  most  generally  useful  and  used  of  the 
second-chromosome  mutants,  first,  because  of  the  perfect  accuracy, 
ease,  and  speed  with  which  the  recessive  character  is  separable  from 
wild-type;  secondly,  because  it  can  be  used  in  experiments  with  any  of 
the  other  second-chromosome  characters  (including  black)  without 
masking  effects  or  confusion  in  the  classification;  thirdly,  on  account 
of  the  value  of  the  position  of  its  gene  near  the  right-hand  end  of  the 
second  chromosome,  speck  being  by  far  the  most  workable  mutant  in 
that  general  region ;  and  finally,  because  its  viabiUty,  its  productivity, 
and  its  fertility  are  above  reproach,  and  it  is  singularly  free  from  such 
bad  habits  as  getting  drowned,  or  stuck  in  the  food,  or  refusing  to  be 
emptied  from  the  culture  bottle,  etc.,  which  alienate  the  affections  of 
the  experimenter  from  certain  other  mutants.  Speck  is  to  be  com- 
mended for  students'  use,  but  care  should  be  taken  that  the  character 
is  clearly  recognized. 

LITERATURE  OF  SPECK. 

The  more  important  papers  referring  to  speck  are:  Morgan,  1910, 
describing  its  origin  and  giving  the  irregular  breeding  results  already 
commented  upon  above;  Sturtevant,  1915,  giving  the  data  of  table  6, 
by  means  of  which  the  locus  of  speck  was  first  worked  out ;  and  MuUer, 
1916,  speck  being  one  of  the  mutants  used  in  the  progeny  test  of  the 
linkage  of  second-chromosome  genes. 


OF   MUTANT   CHARACTERS.  135 

OLIVE. 

ORIGIN  AND  STOCK  OF  OLIVE. 

The  origin  and  eariy  history  of  the  stock  called  "olive,"  because  of  the 
body-color  present,  is  only  partly  a  matter  of  record,  though  the  account 
given  in  the  section  on  speck  is  substantially  correct.  To  repeat :  In 
the  fall  of  1909,  Morgan  started  selection  on  stocks  of  wild  flies  that 
were  throwing  individuals  \vith  extra-dark  trident  patterns.  One  line 
of  selection  eliminated  this  variation,  and  the  resulting  "without "  stock 
represented  the  original  wild  stock  before  the  occurrence  of  the  "  with  " 
mutation.  It  was  in  this  "without"  stock  that  the  old  speck  was 
found.  The  selection  in  the  opposite  direction  isolated  the  third- 
chromosome  semi-dominant  mutation  "with"  (plate  5,  fig.  3).  The 
"olive"  stock  appears  to  have  resulted  from  selection  carried  out  on  a 
stock  different  from  that  which  gave  rise  to  **  with."  The  trident  pat- 
tern of  the  "olive"  stock  is  dark,  but  is  not  distinct,  being  submerged 
in  a  general  olive  color  that  suffuses  the  thorax.  The  "oUve"  stock 
was  obtained  about  May  1910,  and  had  been  kept  in  the  stock  room 
about  a  year  when  it  was  noticed  that  it  was  pure  for  speck. 

CHROMOSOME  AND  LOCUS  OF  OLIVE. 

During  the  fall  and  winter  of  1912  several  crosses  were  carried  out 
by  Miss  Wallace  with  the  "  olive  "  stock.  "  Olive  "  crossed  to  wild  gave 
wild-type  offspring  which  were  inbred  in  pairs  to  give  F2.  This  cross 
and  the  reciprocal  were  both  made  and  gave  the  same  kind  of  Fi  and  F2 
results  in  the  distribution  of  both  characters  and  sex,  showing  that  no 
important  sex-linked  modifiers  of  body-color  were  present.  The  com- 
bined F2  counts  (2,857  flies)  gave  a  very  perfect  9  :  7  ratio  of  gray  to 
"olive"  (1,622  :  1,235),  showing  that  the  "oHve"  stock  contained  two 
recessive  dark  body-colors  whose  genes  assorted  independently  (tables  2 
and  3) .  A  further  separation  of  the  "  olive  "  classes  into  the  component 
two  single  and  the  double  recessive  forms  was  not  attempted.  That 
one  of  the  recessives  (olive  II)  was  carried  in  the  second  chromosome 
was  proved  by  the  strong  linkage  olive  showed  with  speck  (tables  2  and 
3).  There  were  only  2.3  per  cent  of  flies  that  were  speck  not-olive. 
The  whole  observed  distribution  corresponds  to  about  14.3  per  cent  of 
crossing-over  between  speck  and  olive.  It  is  certain  that  this  value  is 
far  too  high  due  to  the  difficulty  in  classifying  the  olive.  Our  later 
experience  has  been  that  olive  is  probably  less  than  a  unit  distance  from 
speck,  and  probably  to  the  right,  which  give  an  approximate  locus  of 
106  when  referred  to  star. 

Very  rarely  have  we  secured  speck  flies  that  we  consider  free  from 
olive.  The  original  stock  of  speck  was  probably  not-olive,  and  in  a 
certain  experiment  made  by  Sturtevant  (1915)  it  seems  likely  that  the 


136  THE    SECOND-CHROMOSOME    GROUP 

great  difficulty  of  classification  was  due  to  a  speck  from  which  olive 
had  been  lost  by  crossing-over.  On  one  other  occasion  speck  has  been 
found  which  seemed  to  be  without  olive.  We  believe  that  most  of  the 
few  flies  classified  as  "speck  not-olive"  in  the  F2  of  olive  by  wild  were 
either  young  flies  in  which  the  olive  was  not  yet  developed  sufficiently 
to  be  surely  classifiable  or  were  fluctuants  extreme  enough  to  cause 
trouble,  neither  of  the  two  olives  being  sufficiently  dark  or  constant  in 
color  to  be  invariably  separable  from  the  wild  type. 

Throughout  our  discussion  of  speck  and  olive  it  has  been  assumed 
that  the  olive  color  which  is  nearly  always  seen  in  speck  flies  is  due  to 
a  separate  gene,  and  while  this  is  probable,  the  evidence  is  by  no  means 
conclusive.  It  may  be  that  the  two  characters  are  the  products  of  a 
single  gene,  and  that  the  supposed  cases  of  "speck  not-oHve"  have 
been  due  on  occasion  to  wrong  classification  of  the  poor  character 
olive,  or  to  the  action  of  minus  modifying  genes,  or  to  a  new  speck 
allelomorph  which  differed  in  this  regard  from  the  old.  A  further 
careful  investigation  would  be  required  to  settle  this  question. 

VALUATION  OF  OLIVE. 

Olive  II  is  of  no  value  for  further  work,  since  the  character  is  not 
sufficiently  distinct  from  wild-type  so  that  the  normal  fluctuations  in 
these  two  body-colors  do  not  overlap,  and  classification  is  accordingly 
both  difficult  and  inaccurate.  Olive  is  subject  to  a  general  objection 
to  the  usefulness  of  all  faint  body-colors,  namely,  the  fact  that  body- 
colors  take  some  time  after  hatching  for  their  full  development,  and  in 
cases  where  the  final  difference  is  not  great  the  intermediate  stages  are 
unpleasant  to  work  with  and  a  source  of  error.  A  further  defect  in 
the  value  of  olive  is  the  uncertainty  as  to  whether  the  character  may 
not  be  found  to  be  only  another  expression  of  the  speck  gene.  Further- 
more, in  case  the  investigation  should  prove  that  two  linked  but  sep- 
arable genes  were  involved,  the  usefulness  of  ohve  would  not  thereby  be 
improved,  since  olive  could  be  used  for  no  purpose  that  could  not  be 
better  met  by  the  use  of  speck  or  one  or  another  of  the  mutations  whose 
genes  are  in  this  same  region.  As  far  as  we  have  been  able  to  observe, 
the  presence  of  oUve  has  had  no  detrimental  effect  upon  the  viabihty 
or  other  qualities  of  speck. 

TRUNCATE  (F). 

(Plate  6,  figures  1  to  6.) 

ORIGIN  OF  TRUNCATE. 

One  of  the  early  mutations  (beaded,  May  1910)  had  been  run  for 
seven  generations  in  stock  cultures  when  a  fly  appeared  (August  1910) 
whose   wings   were   somewhat   obUquely   truncated   and   somewhat 


I' 


4, 


*:: 


tlATE  6 


OF   MUTANT   CHARACTERS.  137 

shorter  than  usual  (Morgan,  1911).  This  fly  when  bred  to  his  wild-type 
sisters  produced  about  10  per  cent  of  offspring  whose  wings  showed  a 
slight  or  moderate  amount  of  truncation  (plate  6,  figs.  4  and  5).  Some 
of  these  truncated  flies  bred  together  produced  in  Fo  nearly  50  per 
cent  of  truncated.  For  several  months  it  was  impossible  by  selection 
to  raise  the  percentage  of  truncates  much  above  50  per  cent,  though 
there  was  an  increase  in  the  shortness  of  the  wings  of  the  truncates 
that  did  occur.  But  later  certain  cultures  gave  much  higher  percentages, 
and  selection  started  at  this  point  and  continued  for  about  a  year  estab- 
Hshed  a  stock  in  which  the  percentage  of  truncates  was  not  far  from  90 
per  cent.     Above  this  level  it  was  impossible  to  maintain  gains. 

Along  with  this  increase  in  the  percentage  of  truncate  individuals, 
several  other  changes  were  observed  to  be  going  on.  There  was  an 
increase  in  the  number  of  flies  which  were  sterile  and  gave  no  off'spring ; 
at  times  about  50  per  cent  of  the  pairs  were  sterile.  There  was  a 
marked  decrease  in  the  productivity  of  those  pairs  which  did  give 
ofifspring.  These  two  facts  made  the  stock  very  difficult  to  carry  on, 
except  in  large  mass  cultures.  In  those  cultures  in  which  the  per- 
centage of  truncates  was  high,  the  amount  of  the  truncation  was  great ; 
i.  e.,  many  of  the  flies  had  extra-short  wings,  some  wings  being  even 
shorter  than  the  abdomen  (plate  6,  figs.  1  and  2).  It  was  found  that 
if  these  short-winged  flies  were  used  in  carrying  on  the  stock,  the  per- 
centage of  truncates  was  higher.  The  flies  whose  wings  were  sHghtly 
truncated  gave  under  90  per  cent  of  truncated,  while  those  flies  whose 
wings  showed  no  truncation  either  gave  no  truncates  or  less  than  or 
about  50  per  cent  of  truncates.  In  all  of  these  cultures  more  of  the 
females  than  of  the  males  showed  the  truncate  character;  that  is, 
truncate  is  ''partially  sex-Umited"  in  its  expression. 

At  this  point  Mr.  E.  Altenburg  took  up  the  selection  of  truncate  and 
confirmed  the  points  just  stated.  Later,  Altenburg  and  Muller  (Mech- 
anism of  Mendelian  Inheritances;  also  mss.)  sought  to  analyze  the 
truncate  stock  by  the  method  of  linkage  to  find  the  cause  of  the  con- 
tinued appearance  of  normal  flies  and  of  the  variations  in  the  extent  of 
the  truncation.  Their  tests  showed  that  truncate  is  primarily  due  to 
a  dominant  gene  in  the  second  chromosome.  This  gene  is  lethal  when 
homozygous,  so  that  pure-breeding  stock  can  not  be  obtained.  When 
heterozygous,  this  gene  is  capable  of  producing  only  a  moderate  trun- 
cation and  fluctuates  in  expression,  so  that  most  of  the  flies  ha\ang  the 
truncate  gene  fail  to  show  the  character  at  all.  But  in  the  selected 
stock  there  are  certainly  two  (one  in  the  first  and  one  in  the  third)  and 
probably  more  genes  whose  effect  is  to  increase  the  amount  of  trunca- 
tion, whereby  both  a  greater  proportion  can  be  detected  and  the  wings 
of  those  which  do  show  truncation  are  shortened. 

Such  intensifiers  could  theoretically  only  raise  the  amount  of  trunca- 
tion to  the  extent  that  every  fly  carrying  the  truncate  gene  can  be 


138  THE   SECOND-CHROMOSOME    GROUP 

distinguished  from  the  wild  tjrpe,  and  because  of  the  lethal  action  of 
the  truncate  gene  this  can  not  exceed  two-thirds  of  the  flies. 

If  some  of  these  modifiers  could  themselves  produce  a  moderate 
truncation,  then  the  percentage  would  pass  beyond  67,  but  there  is 
evidence  that  the  modifiers  are  unable  to  produce  truncation  in  the 
absence  of  the  chief  gene. 

TRUNCATE  LETHAL. 

Since  at  least  one-third  of  the  flies  must  look  like  wild  flies  rather 
than  tnmcates,  their  non-appearance  in  the  highly  selected  stock  is  to 
be  accounted  for  by  the  assumption  of  a  lethal  gene  which  is  carried 
in  the  II  chromosome,  homologous  to  that  carrying  the  truncate 
gene.  This  condition  has  not  been  proved  by  testing,  but  the  action 
of  autosomal  lethals  is  well  understood  and  a  similar  case  of  an  auto- 
somal lethal  giving  an  apparently  pure-breeding  stock  when  balanced 
against  an  autosomal  dominant  which  is  itself  lethal  when  homozygous 
(beaded)  has  been  demonstrated  by  Muller. 

It  is  now  clear  what  is  the  meaning  of  the  early  history  of  the 
truncate  stock  which  was  for  so  long  a  puzzle.  The  original  truncate 
fly  was  heterozygous  for  the  dominant  truncate  gene.  In  a  cross  to 
wild- type  sisters  only  10  per  cent  of  the  offspring  showed  the  truncate 
character,  though  half  of  them  carried  the  truncate  gene.  This  low 
power  of  expression  of  the  character  was  due  to  the  lack  of  effective 
mf)difiers,  most  of  which  were  recessive. 

The  first  period  of  inbreeding  and  selection  resulted  in  the  collect- 
ing of  whatever  modifiers  were  present,  and  by  the  approach  to  homo- 
zygosis  allowed  more  of  the  recessive  ones  to  show  their  effect.  But 
by  such  means  the  proportion  of  truncate  could  not  be  advanced 
beyond  67  per  cent  and  was  not  advanced  much  beyond  50  per  cent. 

The  limit  of  67  per  cent  imposed  by  the  lethal  nature  of  the  primary 
truncate  gene  must  have  been  broken  down  by  the  occurrence  (Febru- 
ary 1911)  of  the  lethal  mutation  in  the  chromosome  homologous  to 
that  carrying  the  primary  truncate  gene.  The  second  period  of  selec- 
tion then  increased  the  percentage  of  truncates  by  increasing  the  preva- 
lence of  this  lethal  in  the  stock.  The  limit  which  this  second  selection 
approached  was  the  condition  in  which  every  second  chromosome 
which  was  not  carrying  the  truncate  gene  should  carry  the  lethal.  By 
this  means  all  the  non-truncate  flies  would  be  eliminated  except  those 
saved  by  crossing-over.  If  the  lethal  were  20  units  away  from  trun- 
cate, measured  along  the  second  chromosome,  then  10  per  cent  of  not- 
truncate  flies  should  survive.  The  very  low  productivity  of  the 
truncate  stock  observed  at  this  time  was  the  result  of  the  action  of  the 
two  lethals — all  homozygous  truncates  as  well  as  all  homozygous 
lethals  dying  as  early  zygotes;  also  the  modifiers  tending  to  produce 
infertility  when  homozygous.     While  the  proportion  of  truncates  was 


OF    MUTANT    CHARACTERS.  139 

limited  at  the  two  values,  67  and  90  per  cent,  the  accumulation  of  the 
modifiers  continued  to  make  the  wings  shorter,  and  the  shortest  indi- 
viduals gave  the  highest  percentage  of  truncates,  since  they  were  on 
the  average  the  ones  carrying  most  modifiers. 

The  increase  in  the  number  of  completely  sterile  individuals  was 
independent  of  the  other  changes  and  due  to  a  mutation  which  occurred 
early  in  the  selection.  Hyde  (1914)  was  able  to  eliminate  this  sterility 
from  the  truncate  stock  by  breeding  for  some  generations  from  those 
families  which  showed  least  sterihty.  But  there  was  no  rise  in  pro- 
ductivity parallel  to  the  ehmination  of  the  sterility.  This  sterility 
behaved  as  a  recessive  in  the  Fi  out-crosses,  and  in  F2  reappeared,  but 
in  such  proportion  and  distribution  as  to  suggest  that  it  also  was 
complex. 

The  fact  that  the  main  gene  for  truncate  is  in  the  second  chromosome 
was  established  by  Muller  and  Altenburg  through  the  non-occurrence 
of  cross-overs  in  back-cross  tests  of  males  heterozygous  for  truncate 
and  black.  In  back-cross  tests  of  similar  females  there  was  somewhat 
under  25  per  cent  of  crossing-over.  A  back-cross  test  showed  that 
there  is  somewhat  over  25  per  cent  of  crossing-over  between  star  and 
truncate,  and  this  information,  in  connection  with  the  known  distance 
of  about  50  between  star  and  black,  showed  that  truncate  is  located 
about  midway  between  star  and  black  and  shghtly  nearer  to  black. 
Since  the  amount  of  data  secured  in  these  tests  is  not  large  and  because 
truncate  is  so  elusive  a  character,  the  location  is  not  precise,  though 
the  locus  is  probably  not  far  from  28  (see  Snub). 

TRUNCATE  REOCCURRENCES. 

Many  of  our  mutant  characters  have  made  their  appearance  more 
than  once,  and  occasionally  under  circumstances  which  make  it  certain 
that  there  has  been  a  new  occurrence  of  the  same  mutative  process 
that  was  responsible  for  the  original  appearance  of  the  character.  In 
other  cases  it  is  probable  that  the  character  is  not  reappearing  because 
of  a  fresh  mutation,  but  that  the  original  mutant  gene  had  been  intro- 
duced in  some  previous  cross  and  has  been  unsuspectedly  present  for 
several  generations  but  has  been  unable  to  appear  because  of  the  way 
in  which  the  crossing  has  been  carried  on.  In  still  other  cases  a  char- 
acter appears  which  resembles  very  closely  another  already  known 
character,  but  the  two  are  the  result  of  mutations  in  entirely  different 
loci  which  are  often  in  different  chromosomes.  Thus,  we  have  at  least 
half  a  dozen  mutant  characters  of  the  "genus"  pink  which  are  so 
similar  as  to  be  practically  indistinguishable  in  mixtures,  yet  which  are 
dependent  on  entirely  distinct  genes.  Characters  of  the  genus  truncato 
are  the  most  frequently  recurring  of  any,  with  the  possible  exception 
of  the  beadeds.  These  two  kinds  of  character  have  both  come  up  in 
the  breeding  work  three  or  four  times  each  year. 


140  THE    SECOND-CHROMOSOME    GROUP 

In  most  of  these  cases  the  character  is  also  "specifically"  truncate, 

and  usually  due  to  the  original  truncate  gene  rather  than  to  a  fresh 

mutation.     In  the  absence  of  its  usual  intensifiers  truncate  may  lurk 

unsuspected  in  a  stock  or  an  experiment  for  many  generations  and  is 

difficult  to  eliminate.     For  this  reason  it  is  practically  impossible  to  be 

certain  in  any  unexpected  case  of  truncate  appearance  that  there  has 

been  a  fresh  mutation.     It  is  not  ordinarily  profitable  to  pay  any 

attention  to  these  appearances  of  truncate,  but  in  two  instances  in 

which,  because  of  the  pedigree,  there  was  less  than  the  usual  likefihood 

that  the  truncate  was  due  to  the  original  gene,  tests  were  made,  and  in 

both  cases  the  character  was  found  to  be  either  truncate  or  else  a  very 

simikir  allelomorph,  though  these  tests  could  throw  no  new  fight  on  the 

question  of  whether  the  gene  were  the  original  or  a  fresh  truncate 

mutation. 

SNUB. 

The  first  of  these  tests  was  made  by  MuUer  (unpubfished).  The 
second  case  appeared  in  the  ninth  generation  of  some  experiments  on 
"duplication."  A  cross  had  been  made  between  a  female  with  the 
new  sex-linked  recessive  wing-character  "cut"  and  a  not-cut  male 
(February  17,  1916,  culture  3338,  Bridges).  AU  the  daughters  were 
expected  to  be  wild-type  and  all  the  sons  cut;  but  9  of  the  77  daughters 
were  seen  to  be  sfightly  truncated,  the  character  being  called  "snub," 
while  some  18  of  the  67  sons  were  cut  with  shortened  and  blunted  wing 
ends  (cut  snub). 

One  of  these  cut-snub  males  outcrossed  to  a  wild  fenoale  gave  about 
a  quarter  of  the  Fi  flies  with  the  snub  or  truncate  character.  This 
result  showed  that  the  character  was  a  dominant,  though  a  "poor" 
one ;  that  is,  not  all  the  flies  genetically  alike  (heterozygotes)  showed 
the  character  somatically.  The  snub  appeared  among  the  Fi  males  as 
well  as  among  the  females,  and  this  fact  showed  that  the  character  was 
non-sex-linked,  for  had  it  been  sex-linked  it  could  have  appeared  only 
among  the  daughters  of  the  above  cross. 

When  snub  flies  were  bred  together,  the  result  was  usually  an  approxi- 
mation to  a  2  snub :  1  not-snub  ratio,  often  with  the  snubs  below  expec- 
tation because  of  the  above-noted  occasional  failure  of  heterozygous 
snubs  to  show  the  character  somatically.  This  ratio  and  the  fact  that 
it  proved  impossible  to  obtain  a  pure-breeding  snub  stock  suggested 
that  the  mutant  was  lethal  when  homozygous,  as  are  most  of  our 
dominants.  In  cut-snub  stock  the  approximation  to  the  2  : 1  ratios 
was  much  closer,  and  it  seems  certain  that  the  character  cut  favors 
the  differentiation  of  snub  (see  cultures  1  to  10,  table  9).  We  are  well 
acquainted  with  such  intensifiers  or  modifiers  in  other  cases,  and 
tnmcate  itself  was  known  to  be  very  susceptible  to  intensification. 
A  few  of  the  cut-snub  pairs  gave  nearly  all  of  the  flies  snub  (see  espe- 
cially 10  and  12,  table  9,  Morgan),  and  it  seems  probable  that  in  these 


OF   MUTANT   CHARACTERS. 


141 


Table  9. — The  offspring 
given  by  pairs  of  cut 
snub  flies  from  the  slock 
of  cut  snub. 


cases  a  lethal  was  present  in  the  homologous  chromosome.  Autosomal 
lethals  are  very  plentiful  and  have  been  clearly  demonstrated  in  many 
other  cases,  though  in  this  case  no  further  test  has  yet  been  made  of  the 
correctness  of  this  explanation. 

That  the  same  kind  of  modifiers  were  present  in  the  snub  stock  as 
were  resopnsible  for  the  short-winged  types  of  truncate  appeared 
certain  from  the  rather  sharp  differences  between  the  cut  snubs  which 
occurred  in  the  inbred  stock.  While  most  of  the  cut  snubs  were  of  the 
type  described,  in  which  the  wing  is  nearly  as  long  as  the  normal  cut 
but  differently  shaped  at  the  tip,  certain  ones  were  much  shorter  and 
the  oblique  truncation  was  very  marked.  These  shorter  ones,  just  as 
in  the  case  of  the  selected  truncate  stock, 
were  most  numerous  in  those  cultures  in 
which  the  expected  2  : 1  ratio  was  most  closely 
approached.  Pair  10  of  table  9  showed  a 
ratio  of  31  short  snubs  to  63  of  medium  or 
slight  truncation  to  46  which  showed  no 
truncation;  this  rather  close  approach  to  a 
1:2:1  ratio  suggested  that  probably  only 
one  such  modifier  was  present  in  the  cross. 

All  of  the  characteristics  of  snub  thus  far 
found  have  agreed  exactly  with  those  of 
"specific"  truncate.  If  it  should  be  found 
that  the  chromosome  locus  of  snub  were  the 
same  as  for  the  original  truncate,  then  we 
should  conclude  that  the  mutation  is  specifi- 
cally truncate. 

Because  of  the  fluctuating  nature  of  the 
dominance  of  snub  and  its  easy  modification, 
a  direct  linkage  experiment  offered  diffi- 
culties.    A  more  exact  method  would  be  to 

establish  the  lethal  nature  of  the  truncate-snub  compound.  This 
could  be  done  by  showing  that  the  Fi  ratio  obtained  by  crossing 
truncate  by  snub  was  a  derivative  of  a  2:1  instead  of  a  3:1  ratio. 
The  observed  ratio  of  174  truncate  to  132  not-truncate  in  the  Fi  from 
this  cross  would  somewhat  favor  the  view  that  the  ratio  is  2  :  1  rather 
than  3:1,  and  that  snub  is  therefore  truncate  (table  10,  Morgan). 
But  here  again  the  uncertainty  that  the  number  actually  showing 
the  truncate  character  would  be  a  close  enough  approach  to  the 
number  heterozygous  for  truncate,  so  that  we  could  decide  whether 
we  were  really  dealing  with  a  2  :  1  or  a  3  :  1  ratio  made  the  results  of 
such  experiments  of  doubtful  value. 

It  was  recalled  that  cut  had  acted  as  an  int^nsifier  of  snub,  so  that  a 
larger  proportion  of  cut  flies  showed  the  snub  character  than  was  the 
case  among  the  not-cut  flies.     Advantage  of  this  fact  was  taken  by 


Culture 
No. 

Cut  snub. 

Cut. 

1 
2 

3 
4 
5 
6 
7 
8 
9 
10 

11 
12 

30 
33 
33 
24 
30 
13 
45 
24 
51 
94 

18 
16 
15 
13 
15 
10 
13 
15 
25 
46 

377 

186 

27 
25 

2 
o 

52 

4 

142 


THE    SECOND-CHROMOSOME    GROUP 


crossing  a  cut-snub  female  to  truncate  males,  in  which  case  all  the  sons 
were  cut.  Among  these  cut  sons  the  ratio  of  snub  to  normal  was  almost 
exactly  2  : 1  (table  11).  The  fact  that  this  experiment  gave  a  close 
approach  to  the  ratio  expected  if  the  truncate-snub  compound  is  lethal 
could  not  be  accepted  as  proving  that  theory,  because  there  might  still 
be  enou42;h  flies  failing  to  show  the  truncation,  so  that  the  ratio  is  really 
the  normal  3  :  1  ratio. 

Table  10. — Fi  ratios  ohtainedfrom  crosses  of  truncate  9  X  snub  cf  {cultures  Itoli), 
and  snub   9    X  truncate  cT   {cultures  6  and  6). 


Culture. 

Truncate- 

Not  trun- 

No. 

like. 

cate-like. 

1 

11 

8 

2 

51 

45 

3 

50 

48 

4 

5 

12 

5 

43 

16 

6 
Total 

14 

3 

174 

132 

Table  11. — Fi  ratios  obtained  from  crosses  of  cut 
snub   9    X  truncate  cT  {pairs). 


1917 

Wild- 

Truncate- 

Cut  d". 

Truncated- 

Jan. 

type  9. 

like  9. 

cut  cf . 

A 

48 

57 

38 

56 

B 

39 

66 

25 

62 

C 

34 

71 

29 

59 

D 

22 

59 

31 

66 

E 

28 

73 

23 

56 

F 

Total 

39 

39 

16 

35 

210 

365 

162 

333 

The  scheme  finally  followed  eliminated  all  classification  of  both 
truncates  and  snubs  and  depended  for  identification  upon  the  readily 
classifiable  character  star  and  upon  the  assumed  lethal  nature  of  the 
truncate-snub  compound.  By  mating  star  to  truncate,  flies  can  be 
obtained  carrying  the  star  gene  in  one  Il-chromosome  and  truncate  in 

^r — Y' )  •    Two  such  flies  mated  together  would  give  a 

2  star  to  1  not-star  ratio,  unless  homozygous  truncate  were  lethal.  But 
since  homozygous  truncate  is  known  to  be  lethal,  this  ratio  becomes 
modified  by  the  death  of  most  of  the  not-star  flies.  A  few  not- 
star  offspring  will  survive  because  of  crossing-over  in  the  female 

There  is  a  precise  relation  between 


( 


+ 


+    r 


+ 


r 


+ 


-) 


the  amount  of  this  crossing-over  and  the  number  of  not-star  flies  which 


OF   MUTANT    CHARACTERS. 


143 


Table  12. 


Culture 
No. 

Stars. 

Not- 
8  tars. 

1 
2 
3 
4 

Total 

199 
264 
300 
187 

27 
21 
84 
17 

950 

149 

appear.     If  x  is  the  percentage  of  cross-over  gametes,  and  lOOx  of 
the  non-cross-over  gametes,  then  the  ratio  of  star  to  not-star  is  200x  :  x. 

Obviously,  if  snub  is  truncate,  then  by  mating  such  a  star-truncate 
heterozygote  by  a  similar  star-snub  heterozygote,  one  should  get  this 
same  200x  :  x  ratio  of  star  to  not-star.  That  is,  the  occurrence  of  a 
ratio  of  star  to  not-stars  in  which  the  not-stars  are  less  numerous  than 
in  the  ordinary  2  :  1  ratio  would  mean  that 
snub  is  truncate,  and  by  calculation  from  the 
observed  ratio  we  can  find  out  how  far  the  locus 
of  truncate  is  from  star.  The  experiment  as 
carried  out  gave  (table  12,  Wallace)  four  cul- 
tures in  which  the  ratio  was  significantly 
different  from  2:1.  The  total  of  stars  was 
950  and  of  not-stars  149,  or  a  ratio  of  6.3  : 1. 
,  From  this  we  may  conclude  that  snub  is 
truncate  or  an  allelomorph  so  similar  in    its 

obvious  characteristics  that  to  demonstrate  a  difference  would  require 
a  refined  biometrical  study  or  elaborate  'interaction'  tests. 

In  table  12  will  be  found  the  ratio  of  star  to  not-star  given  by  crosses 
of  females  heterozygous  for  star  and  truncateto  males  heterozygous 
for  star  and  snub. 

The  solution  of  the  proportion  200x  :  x  :  950  :  149  gives  a  value  of 
27.1  for  x;  that  is,  there  is  27.1  per  cent  of  crossing-over  between  star 
and  truncate.  Nearly  1  per  cent  should  be  allowed  for  double  cross- 
ing-over within  the  distance  from  star  to  truncate,  or  the  map  distance 
should  be  about  28.0  on  the  basis  of  this  data.  This  position  also 
agrees  with  what  is  known  of  the  location  of  truncate. 

INTENSIFICATION  OF  TRUNCATE  BY  CUT. 

That  cut  intensifies  the  original  truncate  in  the  same  manner  as  it 
does  snub  is  sho\\Ti  by  the  results  of  a  test  of  this  point  (table  13). 
When  a  cut  female  was  crossed  to  a  truncate  male  the  ratio  of  not- 
truncate  to  truncate  among  the  males  was  1:0.79;   that  is,  quite  a 

Table  13. — Intensification  of  truncate  by  cut — Pi,  cut  9   X  truncate  cT. 


1917. 
Jan. 

Wild- 
type  9 . 

Trun- 
cate 9  . 

Cut  cT. 

Truncated 

cut  cf . 

I 
II 

Total .  . 

81 
66 

44 
15 

61 
44 

42 
41 

147 

59 

105 

83 

close  approach  to  the  expected  1:1;  but  among  the  sisters,  which 
were  not  cut,  this  ratio  was  1  : 0.40,  which  means  that  about  43  per 
cent  of  the  females  genetically  truncate  failed  to  show  the  character. 
The  intensification  by  cut  is  more  extensive  than  appears  at  first 


9 

d^ 

Wild-type 

"Slight" 

"Long" 

"Intermediate". 
"Short" 

37 
96 
62 
164 
52 

104 
46 
50 

146 
63 

144  THE   SECOND-CHROMOSOME    GROUP 

glance,  because  normally  the  males  show  a  considerably  smaller  per- 
centage of  truncate  than  do  the  females.  The  difference  in  culture 
II  was  especially  striking. 

A   recent  census   of  the  truncate  stock,  Table  14. 

which  has  been  run  for  about  5  years  under 
selection  not  especially  rigorous,  showed 
about  17  per  cent  of  wild-type  flies  (table  14). 
The  truncate  flies  were  of  various  degrees  of 
shortness,  of  which  the  most  frequent  was 
that  known  as  "intermediate"  (correspond- 
ing to  fig.  4  of  Plate  6).     The  very  short 

truncates  were  not  especially  numerous,  although  in  selecting  the 
parents  each  generation  they  had  been  preferred.  Table  14  gives  the 
census  of  truncate  stock  (May  1917). 

BLACK  (h). 

(Plate  5,  figure  2.) 

ORIGIN  OF  BLACK. 

The  first  workable  body-color  mutation,  black,  was  found  by  Morgan, 
October  1910,  in  the  F2  of  a  cross  between  miniature  and  wild  flies 
(Morgan,  1911). 

DESCRIPTION  OF  BLACK. 

When  black  flies  are  freshly  hatched  little  black  color  has  developed 
on  the  body,  though  the  legs  and  feet  are  darker  than  normal.  Within 
a  few  minutes  after  hatching  the  color  has  deepened  so  that  the  head, 
thorax,  and  abdomen  are  a  clean,  fresh,  greenish  black,  more  intense 
on  the  thorax  than  on  other  parts.  This  color  becomes  progressively 
darker  with  age.  The  wings,  after  expanding,  also  become  much 
darker,  and  along  each  side  of  the  veins  a  broad  band  of  pigment  begins 
to  develop  and  becomes  conspicuous  in  old  flies. 

SEMI-DOMINANCE  OF  BLACK. 

While  the  fly  heterozygous  for  black  is  noticeably  darker  than  the 
wild-type,  this  separation  can  not  be  made  completely,  although  it  is 
occasionally  made  use  of  for  special  purposes  (see  sections  on  Jaunty, 
p.  162,  and  Apterous,  p.  237).  Black  is  generally,  therefore,  treated 
as  a  recessive,  and  the  separation  of  black  from  the  heterozygote  is 
easy  and  entirely  accurate. 

CHROMOSOME  CARRYING  BLACK. 

Black  is  a  member  of  the  second-chromosome  group  by  definition. 
As  soon  as  it  had  been  established  that  the  loci  for  the  sex-linked 
mutations  were  capable  of  being  mapped  in  definite  positions  (Sturte- 


OF   MUTANT   CHARACTERS.  145 

vant,  1912),  this  same  procedure  was  applied  to  the  non-sex-linked 
mutations.  The  cytological  work  of  Miss  Stevens  had  shown  that 
there  were  at  least  three  autosomes  in  Drosophila,  and  it  was  expected 
that  a  group  of  linked  genes  would  be  found  to  correspond  to  each  of 
these.  At  this  time  there  were  only  two  non-sex-linked  mutations- 
black  and  pink — whose  inheritance  had  been  worked  out  by  Morgan 
and  whose  behavior  was  definitely  known  to  be  Mendelian  and  normal. 
The  next  point  was  to  estabUsh  the  relation  of  these  mutants  to  each 
other  in  inheritance.  This  was  done  by  raising  an  F2  from  the  cross  of 
black  by  pink.  The  F2  ratio  was  quite  clearly  that  of  independent 
inheritance,  since  it  approximated  9:3:3:1,  with  the  double  reces- 
sive present  in  as  large  numbers  as  expected  (Sturtevant,  February  1 , 
1912).  Sturtevant  soon  showed  by  means  of  back-cross  tests  that 
there  was  no  appreciable  Unkage  between  black  and  pink.  Provision- 
ally, black  and  pink  were  assumed  to  be  in  separate  chromosomes — 
the  second  and  the  third.  The  second  chromosome  is  arbitrarily  that 
chromosome  which  carries  the  gene  for  black,  and  any  other  genes  that 
maybe  found  to  be  Hnked  to  black;  similarly,  the  third  chromosome  is 
defined  as  that  chromosome  which  carries  the  gene  for  pink,  and  all 
other  genes  found  to  be  members  of  the  linkage  group  containing  pink. 
Soon  after  the  black  pink  F2  had  given  the  first  autosomal  inde- 
pendence, an  F2  between  black  and  curved  demonstrated  the  first 
autosomal  linkage.  As  soon  as  this  Hnkage  was  observed  (March  4, 
1912)  definite  plans  were  made  to  test  the  linkage  relations  (chromo- 
some and  locus)  of  all  the  autosomal  mutants  thus  far  found,  making 
full  use  of  the  back-cross  method.  (See  Bridges  and  Sturtevant,  1914, 
p.  205).  By  the  middle  of  July  it  was  known  as  a  result  of  these  tests 
that  besides  black  and  curved,  purple,  vestigial,  balloon,  blistered, 
jaunty,  and  arc  were  in  this  second  chromosome. 

LOCUS  OF  BLACK. 

The  locus  of  black  was  taken  as  the  base  of  reference  in  the  mapping 
of  these  other  genes.  Since  curved  was  the  first  mutant  knowTi  to  be 
in  the  second  chromosome  with  black,  its  locus  determined  the  direction 
along  the  chromosome  which  was  to  be  defined  as  "to  the  right' '  (bUick 
curved).  The  loci  of  all  the  other  mutants  just  mentioned  were  later 
found  to  lie  on  the  same  side  of  black  as  curved  does,  so  that  black  was 
the  locus  farthest  to  the  left,  and  the  natural  zero-point  of  the  map. 
Black  is  now  the  real  base  of  reference  in  the  mapping  of  the  entire 
second  chromosome,  and  all  other  genes  are  plotted  in  relation  to  it, 
either  directly  in  the  case  of  those  genes  nearby  (dachs,  jaunty,  purple, 
vestigial,  etc.),  or  indirectly  by  being  located  with  reference  to  certain 
important  genes  (star,  curved,  speck,  etc.),  whose  positions  \\ith  regard 
to  black  have  been  so  well  estabhshed  that  they  in  turn  can  siifely  be 
used  as  secondary  bases. 


146 


THE    SECOND-CHROMOSOME    GROUP 


Loci. 


Star  black . 


Streak  black 
Dacha  black 


Squat  black.  . 
Black  jaunty. 

Black  purple. 


Table  15. — Summary  of  the  cross-over  data  involving  black. 


Black-// /o 

Black  vestigial 


Total. 


1 ,  .352 
496 
865 
690 

13,104 


16,507 


462 


338 

933 

4,892 

462 


6,725 


82 
462 


773 
3,934 
6,001 

462 

36,622 

2,139 


48,931 


166 


3,499 

1,268 
694 

4,892 

5,001 
462 

450 
2,1.39 

1,74b 

20,153 


Cross- 
overs. 


522 
203 
315 
266 

4,944 


6,250 


120 


82 
163 

874 

77 


1,196 


9 
1? 


38 
212 
322 

26 

2,214 

214 


3,026 


22 


632 

217 
169 

806 

815 

78 

99 
477 

285 
3..57S 


Per- 
cent. 


38.6 
40.9 
36.4 
38.6 

37.7 


37.9 


26.0 


24.3 
17.5 
17.9 
16.7 


17.8 


Date. 


Jan.  11.  1915 
Oct.  23,  1915 
Oct.  26,  1915 
Dec.  22,  1915 

Dec.  5,  1916 


11.0 
0.2? 


4.9 
5.4 
6.4 
5.6 
6.0 
10.0 


6.2 


13.0 


18.1 

17.1 
24.4 

16.5 

16.3 
16.9 

22.0 
22.3 

16.3 

17.8 


May  — ,  1914 

Mar.  18,  1913 
June  30,  1913 
Dec.  10,  1913 
May  — ,  1914 


Apr.  3,  1911 
May  — ,  1914 

Dec.  12,  1912 
Aug.  28,  1913 
Jan.  9,  1914 
May  — ,  1914 
Jan.  5,  1915 
Mar.    5.  1917 


Jan. 15,   1916 

Sept.  10,  1912 

Sept.  10,  1912 
June    8, 1913 

Dec.  10,  1913 

.Jan.     9,  1914 
May  — ,  1914 

Nov.  17,  1915 
Mar.    5,  1917 

May  — .  1917 


By  — 


Reference. 


Bridges.  . 
Do. 
Do. 
Do. 

Plough .  .  .  ■ 


Muller . 


Bridges . . . 

Do. 

Do. 
Muller . . . 


Bridges .  . . 
Muller 


^*'       b  vx 


B.C.;  1921-'24. 


ft; 


b  fr 


B.C.;  2282-'84. 


Pg".    .     ^  B.C. ;  table  123,  this  pape 


du- 


S'  di 


B.C.;  2679-7085. 


J.  E.  Z.,  '17,  p.  147;   temperature 

S' 

— ^  B.C.;    tables    7    (22°),   8 

(27°),  8«  (22°),  111  (22°),  17,. 


Am.  Nat.,  '16.  p.  422. 

d;  d  b  F2;  II  34-36. 

d;  d  b  B.C.;  II  40-11  98r. 

d,- d  6 r)^  balanced  B.C.;  II 114-11 13 

Am.  Nat.  '16,  p.  422. 


Sq: 


Sq 


B.C.;  4044. 


Bridges . . . 

Do. 

Do. 
Muller .... 
Plough.  .  . 

Do. 


Bridges . . .  . 

Morgan  .  .  . 

Do. 

Sturtevant . 

Bridges . . .  . 

Do. 

Muller 


Bridges . . 
Plough.  . 
Gostenhofer 


b  Px 
Am.  Nat.  '16,  p.  422. 

pr;  b  pr  B.C.;  C  174-11  2. 

pr;  bprc  B.C.;  Ists;  II  58-11  88. 

pr;  b  Pr^V  balanced  B.C.;  II141-6'3 

Am.  Nat.  '16,  p.  422. 

J.  E.  Z.,  '17,  total  bprC  B.C. 

J.  E.  Z.,  '17,  total  b  Pr  Vg  B.C. 


hia;  b  liia  F2;"2840,  '59,  '63. 

b 
Biol.  Bull.  '14,  p.  197;   — "  B.C. 

Vg 

Biol.  Bull.  '14,  p.  198;  b  Vg  B.C. 
Zeit.  f.  i.  A.  u.  V.'15,  p.  286;  b  Vg 

balanced  B.C. 
d;  d  b  Vg  balanced  B.C.;  II  11^ 

II  138. 

Pr;  b  Pr  Vg  balanced  B.C. ;  II  141-6' 
Am.  Nat.  '16,  p.  422. 

<S' 
vj*;  "T — n  B.C. ;  table  123,  this  pap 

"  b  Vg  I 

J.  E.  Z.,  '17,  b  Pr  Vg  B.C. 

b 

B.C.;  students'  records. 


OF    MUTANT   CHARACTERS. 


147 


Table  15. — Summary  of  cross-over  data  involving  black — continued. 


Loci. 


ack  curved. 


lack  plexus  . 


lack  fringed 
lack  arc ... . 


lack  blistered 

lack  pinkish  . 
lack  speck .  .  . 


ack  balloon  . 


ack  morula 


Total. 

Cross- 
overs. 

Per- 
cent 

7,419 

1,717 

23.1 

260 

69 

25.5 

253 

66 

26.1 

402 

120 

29.9 

3,934 
223 

839 
63 

21.3 

28.2 

462 
36,622 

106 

8,598 

22.9 
23.4 

13,104 

2,659 

20.3 

62,679 

14,237 

22.7 

1,026 

417 

40.6 

1,352 

576 

42.6 

82 

38 

46.4 

2,460 

1,031 

41.9 

496 

211 

42.5 

798 
6,794 

286 
2,951 

35.9 
43.4 

7,592 

3,237 

42.6 

224 

93 

41.5 

736 
223 

371 
110 

51.4 
49.3 

462 

216 

46.8 

685 

326 

47.6 

1,774 
462 

857 
216 

48.3 
46.8 

2,236 

1.073 

48.1 

755 
6,794 

353 
3,165 

46.1 
46.6 

7,549 

3,518 

46.6 

Date. 


Jan. 13, 1913 

Jan. 13.  1913 

Jan.  13, 1913 

June    8. 1913 

Aug.  24.  1913 
Oct.  16,  1913 

May  — .  1914 
Jan.     5,  1915 

Dec.  13,  1915 


Jan.     1, 1915 
July  20.  1915 

Apr.    3.  1916 

Oct.  23,  1915 

Dec.  13.  1912 
Aug.    4,  1914 

Nov.    4,  1913 

Sept.  23,  1914 
Oct.   16,  1913 

May  — ,  1914 


Mar.  29,  1913 
May  — ,  1914 


Sept.  28.  1913 
Aug.    4,  1914 


By- 


B.  &  Stutt. 

Do. 

Do. 
Sturtevant . 

Bridges .... 
Sturtevant. 


Muller. 
Plough . 


Plough .  .  .  . 

Bridges . . . . 
Do. 

Do. 

Bridges . . .  . 

Bridges . . .  . 
Do. 

Bridges. . .  . 

Do. 

Sturtevant . 

Muller 


Reference. 


Biol.  Bull.  '14.  p.  209;  fe  c  and  —  B.C. 

Biol.  Bull.  '14.  p.  208;  6  c  Fi. 

h 

Biol.  Bull.  '14.  p.  212,  —  B.C. 

c 

Zeit.  f.  I.    A.    u.    v.;    'la.    p.    247; 

bVfC  B.C. 
Pr;  b  pr  c  B.C.;  lata;  II5H-II88. 
Zeit.   f.   L   A.   u.   v..   '15.   p.   247, 

b  c  Sp  B.C. 
Am.  Nat.  '16.  p.  422. 
J.  E.  Z.  '17,  h  p,  c  B.C.  totals. 

S' 


J.  E.  Z.  '17 


6  c 


B.C.  controls. 


Px;b  p,  B.C.;  1084-'99. 

S' 

B.C.;  1921-24. 


px; 


b  Px 


Sn: 


Sa 


b  Px 


B.C.;  4044. 


Sturtevant . 
Muller  .  . . . 


Bridges . . 
Do. 


fr: 


bf, 


B.C.;  2282-'84. 


a;  6  a  B.C.;  C  172-11  3. 

m,;  b  a  nif  balanced  B.C.;  364 


h»: 


Bs 


B.C.;  II  102- 


Pinkish;  h  pinkish  B.C.;  525-2426. 
Zeit.   f.   I.   A.   u.   V.    '15,   p.   247. 

b  c  Sp  B.C. 
Am.  Nat.  '16.  p.  422. 


Zeit.  f.  I.  A.  u.  V.  '15.  p.  276;  B.C. 


m,:bmrYi.C.\  II  93-11  96. 
mp  6  am,  balanced  B.C.;  364. 


The  zero  position  in  the  second  chromosome  has  been  delegated  to 
star,  which  is  found  to  be  46.5  units  to  the  left  of  black,  that  is,  black  is 
at  an  approximate  position  of  46.5  on  the  map  as  recast  with  star  as  the 
zero-point.  Table  15  gives  a  summary  of  all  the  cross-over  data 
previously  published  as  well  as  that  given  in  other  sections  of  this  paper. 


148  THE   SECOND-CHROMOSOME    GROUP 

"BROWN"  BODY-COLOR. 

Soon  after  the  discovery  of  black,  there  appeared  in  the  black  stock 
a  few  males  whose  color  is  a  rich  "brown"  instead  of  being  a  clear, 
cold,  greenish  black.  These  flies  were  in  reaUty  a  double  recessive,  as 
was  shown  by  the  F2  results  from  the  out-crossing  of  these  males  to 
wild  females.  The  other  recessive  turned  out  to  be  "yellow,"  which 
is  sex-linked.  An  astounding  number  of  flies  (hundreds  of  thousands) 
were  raised  (by  Morgan,  Wallace,  Bridges,  and  Eleth  Cattell)  in  work- 
ing out  the  simple  relation  of  brown  to  black,  to  yellow,  and  to  the 
wild  form.  A  similar  interest  was  shown  in  the  relations  of  vermilion 
and  pink  (the  double  recessive  being  called  "orange"),  these  relations 
being  then  regarded  as  highly  important  from  the  standpoint  of  the 
presence-and-absence  theory  and  the  seriation  of  characters. 

VALUATION. 

Black  is  a  mutation  of  first  rank  in  value,  and  has  been  used  more 
extensively  than  any  other  autosomal  character.  Its  viability  is 
excellent.  With  a  little  practice  black  can  be  separated  from  the 
heterozygous  form  with  perfect  accuracy.  There  are  no  other  body- 
color  mutations  in  the  second-chromosome  that  interfere  with  the 
classification  of  black,  and  in  turn  black  can  be  used  in  experiments 
with  any  of  them  (including  speck  and  streak)  without  masking  effects 
or  confusion.  Black  has  been  extensively  used  in  class  work  in 
genetics  by  beginners ;  in  this  case  the  only  caution  necessary  is  in  the 
classification  of  very  young  flies,  since  the  full  black  color  is  slow  to 
develop.  Even  experienced  workers  occasionally  put  back  into  the 
culture-bottle  the  very  young  flies  (in  a  cornucopia,  if  etherized), 
and  then  classify  them  when  they  are  again  taken  out  at  the  next 
counting. 

BALLOON  (bj, 

(Plate  7,  figure  1.) 

The  mutant  character  balloon  was  found  by  Morgan  (November 
1910)  in  a  stock  culture  of  truncate  flies  (Morgan,  1911).  This  char- 
acter was  first  noticed  from  the  fact  that  certain  flies  not  long  emerged 
from  the  pupa-case  had  their  wings  pumped  full  of  Uquid,  the  two 
laminae  of  the  wing  being  separated,  except  at  the  edges,  to  form  a 
balloon  (plate  7,  fig.  1).  As  these  flies  became  older  these  vesicles 
usually  broke  or  the  liquid  was  resorbed,  so  that  the  laminae  came 
together,  giving  an  uneven  or  blistered  appearance  to  the  wing.  These 
wings  were  held  out  at  a  wide  angle  from  the  body  (plate  7,  fig.  1)  and 
this  character  forms  the  most  quickly  recognizable  mark  of  identifi- 
cation in  the  separations.  The  divergence  of  the  wings  serves  well  for 
a  quick  and  rough  preliminary  separation,  though  a  more  reliable 


PLATE  7 


OF   MUTANT   CHARACTERS.  149 

character  is  the  presence  of  extra  veins  in  the  wings,  which  should  be 
looked  for  in  checking  up  whether  any  balloon  flies  with  only  slight 
divergence  have  been  passed  over  in  the  preliminary  separati(jn. 
These  extra  veins  are  most  plentiful  as  a  plexus  about  the  posterior 
cross-vein  and  also  between  the  marginal  and  second  longitudinal 
veins  (plate  7,  fig.  1).  The  balloon  wing  is  usually  considerably  smaller 
than  normal  and  is  of  a  brownish  uneven  color  and  of  markedly  chiti- 
nous  appearance.  The  balloon  flies  run  about  very  actively  and  take 
short,  quick  jumps,  but  are  unable  to  fly. 

Since  balloon  appeared  in  truncate  stock  it  partook  of  the  sterility  of 
truncate.  By  out-crossing  and  extraction  a  stock  was  obtained  which 
was  fully  fertile  and  which  was  free  from  truncate. 

CHROMOSOME  OF  BALLOON. 

That  the  gene  for  balloon  is  in  the  second  chromosome  was  shown 
by  Sturtevant  (April  20,  1912)  by  means  of  a  cross  to  curved,  which 
gave  in  F2  the  2:1  : 1  : 0  ratio  typical  in  Drosophila  for  experiments 
with  genes  in  different  homologues  of  the  same  chromosome  pair. 

LOCUS  OF  BALLOON. 

Sturtevant  also  found  that  the  locus  of  balloon  is  very  far  away 
from  that  for  black  (black  balloon  cross-over  value  48.3),  and  is  in  fact 
in  the  right-hand  end  in  the  same  region  with  speck.  Speck  and  bal- 
loon were  found  to  be  so  close  together  that  all  attempts  to  synthesize 
the  double  recessive,  speck  balloon,  failed.  Without  this  double 
recessive  it  was  impossible  to  run  a  back-cross  test  which  would  have 
told  on  which  side  of  speck  the  balloon  gene  is  situated  and  exactly 
how  far  distant. 

By  the  laborious  method  of  testing  individually  the  offspring  of 

females  heterozygous  for  speck  and  balloon  ( irh')  ^'^"^^^r  (1916) 

found  that  two^  individuals  out  of  a  total  of  462  represented  crossing 
over  between  speck  and  balloon.  Balloon  is  therefore  about  0.4  unit 
away  from  speck,  and  to  the  right  as  was  shown  by  the  other  second- 
chromosome  characters  tested  at  the  same  time. 

On  account  of  its  marked  variability,  the  character  balloon  has  been 
used  by  Marshall  and  Muller  (1917)  in  a  study  of  the  question  of  the 
contamination  of  a  gene  by  its  allelomorph  when  the  two  are  present 
in  the  heterozygote.  By  back-crossing  in  each  generation  a  male 
heterozygous  for  balloon,  and  for  certain  other  characters  used  as 
indexes,  to  a  female  which  has  these  index  characters  but  is  free  from 
balloon,  a  stock  was  carried  on  for  some  50  generations  (nearly  3  years), 

'These  two  cross-overs  were  inadvertently  omitted  from  the  table  of  page  422  (Muller  1916) 
and  from  his  summary  on  page  423. 


150 


THE   SECOND-CHROMOSOME    GROUP 


during  which  time  the  balloon  gene  was  constantly  maintained  in 
heterozygous  condition.  If  the  effect  of  the  not-balloon  gene  always 
present  in  the  homologous  chromosome  were  to  render  the  balloon 
gene  less  characteristically  balloon-producing,  then  the  balloon  stock 
finally  extracted  from  this  long-continued  heterozygosis  should  exhibit 
a  lower  grade  of  the  balloon  character  than  that  shown  by  the  regular 
stock  of  balloon  which  for  some  5  years  had  been  kept  homozygous  by 
inbreeding,  ^^^len  the  average  grade  of  the  individuals  of  a  stock 
freshly  extracted  from  this  heterozygous  condition  was  determined  and 
compared  with  the  Hke  grade  determined  for  the  homozygous  stock, 
it  was  found  that  the  difference  from  normal  of  the  outcrossed  type 
was  not  less  than  the  difference  of  the  inbred  stock.  A  comparison 
of  the  standard  deviations  of  these  two  stocks  showed  that  there  had 
been  no  increase  in  variability  on  account  of  the  continued  heterozy- 
gosis. These  facts  together  showed  that,  in  an  adequately  tested  case 
of  character  variability,  contamination  of  genes  was  not  operative  to 
a  detectable  degree. 

A  summary  of  the  linkage  data  involving  balloon  is  given  in  table  16. 

Table  16. — Summary  of  data  upon  linkage  of  balloon  with  other  second- 
chromosome  loci. 


Loci. 

Total. 

Cross- 
overs. 

Per 
cent. 

Date. 

By— 

Reference. 

Streak  balloon . . . 
Dachs  balloon .  .  . 
Black  balloon  . . . 

Purple  balloon . . . 
Vestigial  balloon. 
Curved  balloon.  . 
Speck  balloon.|. .  . 

462 

462 

1,774 

462 

242 
231 

857 

216 

52.3 
50.0 
48.3 

46.8 

May—,  1914 
May—,  1914 
Mar.  29,  1913 

May  — ,  1914 

May—,  1914 
May—.  1914 
May—,  1914 
May  — ,  1914 

Muller 

Do. 

Sturtevant . 

Muller 

Muller 

Do. 
Do. 
Do. 

Am.  Nat.,  1916,  p.  422. 

Do. 
Zeit.f.i.  A.  u.  v.,  1915, 

p.  276,  B.C. 
Am.  Nat.,  1916,  p.  422. 

Am.Nat.,1916,p,422. 
Do. 
Do. 
Do. 

2,236 

1,073 

48.1 

462 
462 
462 
462 

218 

178 

150 

2 

47.4 

38.5 

32.5 

0.4 

VESTIGIAL  (O. 

(Plate  7,  figure  2.) 

ORIGIN  AND  DESCRIPTION  OF  VESTIGIAL. 

The  mutant  wing-character  now  called  vestigial  was  found  by  Mor- 
gan (December  1910)  in  a  stock  culture  of  truncate  flies  (Morgan,  1911). 
A  few  flies  of  both  sexes  were  found  which  seemed  to  have  tiny  scales 
in  place  of  wings.  The  size  of  the  vestigial  wing  in  relation  to  the  size 
of  the  body,  and  the  characteristic  manner  in  which  these  wings  are 
held  out  at  right  angles  to  the  body  instead  of  l3ang  back  above  the 
abdomen,  are  shown  by  the  figure.  The  character  was  at  first  called 
"wingless,"  and  this  name  appeared  in  the  first  few  publications 


OF   MUTANT    CHARACTERS.  151 

describing  it  (Morgan,  1911 ;  Morgan  and  Lynch,  1912;  Morgan,  1912). 
The  name  "vestigial"  was  adopted  when  it  was  found  that  the  "scale" 
was  the  remaining  basal  portion  of  the  normal  wing  with  the  venation 
characteristic  of  that  region  (plate  7,  fig.  2).  The  enormous  reduction 
in  the  size  of  the  wing  is  mainly  due  to  the  trimming  away  of  the  ter- 
minal and  marginal  regions  of  the  wing.  There  is  a  marked  uniformity 
in  the  extent  of  this  trimming  and  in  the  character  of  the  venation  ves- 
tiges. Most  commonly  the  wing  is  trimmed  away  as  far  as  the  anterior 
cross- vein,  which  in  many  specimens  follows  the  new  margin.  The  true 
marginal  vein  with  its  characteristic  chaetae  is  entirely  removed.  The 
basal  parts  of  all  five  longitudinal  veins  are  easily  recognizable,  and  have 
their  normal  relationship  and  junctures  with  one  another.  Certain 
small  veins  at  the  base  of  the  wing  are  represented  here  as  in  the  normal 
wing.  The  vestigial  wing  is  ordinarily  held  out  at  right  angles  to  the 
body,  probably  because  of  the  relative  thickness  of  the  posterior  margin 
of  the  wing.  Sometimes,  however,  the  ends  of  the  wings  are  bent 
sharply  backward.  These  wings  seem  to  be  cut  ofif  in  a  squarer  fashion 
than  the  normal  vestigial  wing.  It  is  not  known  whether  this  varia- 
tion has  any  hereditary  significance.  The  "balancers"  of  vestigial 
flies  are  affected  in  a  way  analogous  to  the  wings.  The  basal  segment 
is  little  afifected,  except  that  it  is  slightly  shorter  and  smaller.  The 
second  segment  is  much  reduced  in  size  and  in  apparent  complexity. 
The  terminal  segment  shows  the  greatest  reduction,  becoming  a  barely 
discernible  pip  (plate  7,  fig.  2)  instead  of  the  balloon-hke  segment 
which  is  the  largest  part  of  the  normal  balancer  (see  plate  7,  fig.  1). 
Another  constant  feature  of  vestigial  flies  is  that  the  two  rearmost 
bristles  on  the  scutellum  are  separated  a  little  wider  than  normal  and 
are  erect  (plate  7,  fig.  2)  instead  of  turning  backwards  (plate  7, 
fig.  3).  Occasionally  vestigial  wings  are  somewhat  longer  than  is  tj-pi- 
cal  and  it  is  probable  that  this  lengthening  is  more  frequent  during 
hot  weather.^  The  vestigial  flies  are  sometimes  inactive,  but  at  other 
times  run  about  very  actively,  appearing  much  like  ants.  Special  care 
has  to  be  taken  with  experimental  cultures  involving  vestigial  to  see 
that  the  vestigial  flies  are  all  shaken  out,  since  they  chng  fast  to  the 
food  or  paper  in  the  culture  bottle  and  are  exceptionally  slow  and 
difficult  to  get  out.  The  viability  of  vestigial  flies  is  fairly  good,  very 
close  approaches  to  expectation  being  obtainable  when  pairs  are  used 
and  food  conditions  are  favorable.  The  earlier  work  showed  consider- 
able deviations  from  expectation  because  of  failure  to  recognize  the 
necessity  of  these  conditions.  Vestigial  flies  tend  to  hat  ch  two  t)r  more 
days  later  than  the  not-vestigial  flies,  and  unless  the  cultures  are  run 
full  term  will  give  ratios  in  which  the  numbers  of  vestigial  are  below 
expectation. 

*  Since  the  above  was  written,  Roberts  (J.  E.  Z.,  191S)  has  strikingly  confirmed  the  fact  that 
high  temperature  favors  the  production  of  wings  approaching  the  wild-type  in  siie. 


152  THE   SECOND-CHROMOSOME    GROUP 

STOCK  OF  VESTIGIAL. 

Since  vestigLal,  like  balloon,  appeared  in  the  truncate  stock,  the 
vestigial  flies  were  often  at  the  same  time  truncate,  though  these  could 
not  be  distinguished  by  inspection  from  the  simple  vestigials.  By  out- 
crossing and  extraction  a  stock  was  obtained  which  seemed  to  be  free 
from  truncate  (as  judged  by  the  absence  of  truncates  among  the  not- 
vestigial  flies  of  certain  Fi  and  F2  cultures).  The  balloon 'mutation 
which  had  appeared  in  the  truncate  stock  just  before  the  occurrence  of 
vestigial  was  even  more  difficult  to  eliminate  and  occasionally  cropped 
out  in  the  early  experiments  in  which  vestigial  was  used. 

INHERITANCE  OF  VESTIGIAL. 

In  out-crosses  to  wild  the  vestigial  appeared  to  be  completely  reces- 
sive. In  F2  the  vestigials  reappeared  in  much  less  than  a  quarter  of 
the  flies,  due  to  the  practice  of  using  mass  cultures  and  to  the  rather 
poor  feeding  methods  of  that  time.  Reciprocal  crosses  gave  the  same 
results  in  Fi  and  F2,  so  that  the  gene  was  known  to  be  not  sex-linked. 

Lutz  (1913)  made  a  biometrical  study  of  wing-length  and  found  that 
the  wings  of  flies  heterozygous  for  vestigial  are  slightly  but  actually 
shorter  than  the  wings  of  ^"ild  flies.  Also,  the  ratio  of  wing-length  to 
femur-length  was  less,  showing  that  vestigial  is  not  completely  reces- 
sive. It  is  known  in  other  cases  also  (see  Morgan  and  Bridges,  1913) 
that  characters  that  to  simple  inspection  are  completely  recessive 
really  are  influencing  the  character  of  the  heterozygous  individuals. 

CHROMOSOME  CARRYING  VESTIGIAL. 

At  this  time  the  only  case  of  autosomal  linkage  known  in  Drosophila 
was  the  observation  by  Bridges  that  no  black  curved  flies  had  appeared 
in  the  Fa  of  the  cross  of  black  by  curved  (Bridges  and  Sturtevant, 
1914).  Following  this,  a  concerted  testing  of  the  linkage  relations  of 
all  the  known  autosomal  mutations  was  carried  out.  One  of  these 
tests,  made  by  Sturtevant  and  by  Miss  Clara  J.  Lynch,  showed  that 
in  the  F2  of  the  cross  of  black  by  vestigial  no  black  vestigial  flies 
api)eared.  Both  of  these  cases  were  put  down  as  very  close  Unkage, 
"complete  repulsion,"  since  it  was  not  yet  known  that  there  is  no 
crossing-over  in  the  male  whereby  this  result  would  be  obtained,  even 
though  the  crossing-over  in  the  female  were  very  free.  That  crossing- 
over  actually  had  occurred  was  shown  by  the  results  of  mating  some 
of  the  F2  black  by  some  of  the  F2  vestigial  flies.  In  one  of  these  F3 
cultures  some  black  flies  occurred,  which  meant  that  at  least  one  of 

the  vestigial  parents  had  been  heterozygous  for  black,  ^ — - ,  the  b  v. 

0  Vn 


a 


OF    MUTANT    CHARACTERS.  153 

chromosome  being  a  cross-over.  By  breeding  together  some  of  these 
F3  blacks,  in  F4  black  vestigial  flies  were  obtained  from  which  a  stock 
was  made  that  is  still  running. 

LOCUS  OF  VESTIGIAL. 

By  aid  of  this  stock  of  black-vestigial  it  was  possible  to  make  back- 
cross  tests  of  the  amount  of  crossing-over.  When  these  experiments 
were  carried  out  by  Morgan  it  was  found  that  there  was  about  22  i)or 
cent  of  crossing-over  in  the  female,  but  none  whatever  in  the  male 
(Morgan,  1912).  The  principle  of  no-crossing-over  in  the  male, 
first  clearly  demonstrated  in  the  above  back-cross,  has  been  found 
to  apply  to  all  cases  in  both  the  second  and  third  chromosomes  of 
Drosophila. 

From  the  early  data  of  Morgan  it  was  known  that  the  two  loci, 
black  and  vestigial,  were  about  22  units  from  each  other.  Several 
errors  have  been  found  in  the  data  for  crossing-over  as  first  presented 
(Morgan,  1912).  These  data,  as  corrected  and  considerably  added  to 
(Morgan,  1914),  show  that  the  locus  of  vestigial  is  about  18  rather  than 
22  units  from  black. 

The  mapping  of  vestigia^l  in  relation  to  the  other  second-chromosome 
genes  was  carried  out  by  Bridges  (through  the  use  of  purple  as  a  sec- 
ondary base)  and  by  Sturtevant  (through  use  of  curved  as  a  base  of 
reference) .  Relatively  large  amounts  of  data  involving  the  relation  of 
vestigial  and  other  second-chromosome  mutants  was  soon  secured. 
The  most  useful  of  these  determina,tions  have  been  the  various  purple- 
vestigial  data,  for  purple  is  the  base  of  reference  for  vestigial.  Table  17 
gives  a  summary  of  this  early  data  and  of  all  that  have  since  become 
available. 

VALUATION  OF  VESTIGIAL. 

Vestigial,  while  it  is  not  strictly  of  first  rank  in  usefulness,  approaches 
very  close  to  this  standard.  In  ease  and  quickness  of  separation  from 
the  wild-type  it  is  unsurpassed.  Its  position  in  the  chromosome  is 
one  which  is  important  and  convenient.  Enough  work  has  been  done 
using  vestigial  as  material,  so  that  in  undertaking  fresh  work  one  can 
count  on  a  sound  basis  for  comparison.  Its  viabiUty  is  good  under 
good  cultural  conditions.  The  above  are  the  points  in  its  favor;  its 
disadvantages  are  that  it  masks  all  other  wing-characters,  so  that  its 
use  in  an  experiment  materially  reduces  the  avaihibility  of  other  \\ing- 
characters,  some  of  which,  such  as  curved,  are  themselves  of  first  rank. 
Its  viabilty  is  apt  to  be  poor  unless  careful  and  experienced  attention 
is  given  to  cultural  conditions,  and  its  lateness  of  hatching  and  the  diffi- 
culty of  getting  the  vestigials  out  of  the  culture  bottle  also  tend  to 
give  aberrant  ratios  to  the  unwary. 


154 


THE    SECOND-CHROMOSOME    GROUP 


Table  17. — Summary  of  cross-over  data  involving  vestigial  and  other  second- 
chromosome  loci. 


Ivoci. 


Star  vestigial . . 
Streak  vestigial 
Dachs  vestigial 


Black  vestigial 


Purple  vestigial 


Vestigial  curved 


Vestigial  speck 


Total. 


450 
462 


4,892 
462 


5,354 


3,499 

1,268 
694 

4,892 

5,001 

450 
2,139 
1,748 


20,153 


825 
2,839 


2,335 

6,001 

462 

2,139 


13,601 


856 
402 
462 


1,720 


1,446 
146 
462 

2,054 


Cross- 
overs. 


195 
164 


1,456 
129 


1.585 


632 

217 
169 

806 

815 

99 

477 
285 


3,578 


79 
305 

303 

539 

60 

323 


1,609 


75 
32 
34 


141 


520 

40 

178 

738 


Per 

cent. 


43.3 
35.5 


29.7 
27.9 


29.6 


18.1 

17.1 
24.4 

16.5 

16.3 

22.0 

22.3 

16.3 


17.8 


9.1 
10.7 

13.0 

10.8 
13.0 
15.1 


11.8 


8.8 
8.0 
7.4 


8.2 


36.0 
27.4 
38.5 

35.9 


Date. 


Nov.  17, 1915 
May  — .  1914 

Dec.  10.  1913 

May  — ,  1914 

Sept.  10,  1912 

Sept.  10,  1912 
June    8, 1913 

Dec.  10,  1913 

Jan.     9,  1914 

Nov.  17, 1915 
Mar.  5,  1917 
May  — ,  1917 


July  16,  1912 
July    5,1913 

July    5,  1913 

Jan.  9, 1914 
May  — ,  1914 
Mar.    5,  1917 


Mar.  14,  1913 
June  8, 1913 
May  — ,  1914 


Mar.  14, 1913 
Sept.  — ,  1914 
May  — ,  1914 


By- 


Bridges  . 
Muller.. 

Bridges. 

Muller. , 


Morgan  .  . 

....Do... 

Sturtevant 

Bridges . . . 

Muller 

Bridges . . . 
Plough . .  . 
Gostenhofer 


Bridges .... 
....Do.... 

....Do.... 

....Do.... 

Muller 

Plough .... 

Sturtevant . 
....Do.... 
Muller 

Sturtevant . 
....Do.... 
Muller 


Reference. 


1  «• 

0  • 


S' 


T — s  B.C. ;  table  123,  this  papei 

O  Vg 

Am.  Nat.,  1916,  p.  422. 

a;  d  h  Vg  balanced  B.C.;  II   Hi- 
ll 138. 
Am.  Nat.,  1916,  p.  422. 


Biol.  Bui.,  1914,  p.  197;  B.C 

Vg 

Biol.  Bull.,  1914,  p.  198;  6  Vg  B.C. 
Zeit.  f.  i.  A.  u.  V.,  1915,  p.  286, 

hvgc  B.C. 
d;  d  b  vg  balanced  B.C.;  II  Hi- 
ll 138. 
Am.  Nat.,  1916,  p.  422. 

«   ^' 
"?  '■  T — B  B.C. ;  table  123,  this  pap« 

O   Vg  ^^ 

J.  E.  Z.,  1917;  bprVgB.C. 

b 

B.C.;  students  records. 


Pr;  Pt  Vg  B.C.;  B  36.1-B  39.2. 
Pr;  Pr  Vg  B.C.  1st;  DA-DH. 

Pr 


pr; 


Vg 


B.C.  1st;  DI-DO. 


Pr!  b  Pr  Vg  balanced  B.C.,  II  141-67< 
Am.  Nat.,  1916,  p.  422. 
J.  E.  Z.;  1917,  bprVg  B.C. 


Zeit.  f.  i.  A.  u.  v.,  1915,  p.  245,| 

Vg  c  B.C. 

Zeit  f.  i.  A.  u.  V.,   1915,  p.  247,i 

Vg  C  Sp  B.C. 

Am.  Nat.,  1916,  p.  422. 


Zeit.  f.  i.  A.  u.  v.,  1915.  p.  245. 
Zeit.  f.  i.  A.  u.  V.,  1915,  p.  287. 
Am.  Nat.,  1916,  p.  422. 


OF   MUTANT   CHARACTERS. 


155 


BLISTERED  (b,). 

(Text-figure  74.) 

ORIGIN  AND  DESCRIPTION  OF  BLISTERED. 

The  mutation  ''blistered"^  was  found  by  Bridges   (November  16, 
1911)  in  a  mixed  stock  of  rudimentary  and  normal  (culture  A23)  as  a 


Costa,  or  marginal  vdn 


ongiiudinal  vein 


Text-figure  74. — Blistered  wing  and  venation.  74a  shows  a  pair  of  wings  with  the  l)end  in  the 
fourth  longitudinal  vein,  and  extra  veins.  746  shows  the  plexus  near  the  end  of  the  fifth 
longitudinal  vein.  74c  shows  for  comparison  a  normal  wing  with  the  standard  terminology 
for  venation  and  for  the  cells  of  the  wing.  It  is  probable  that  74c  is  on  a  larger  scale  than 
74a  and  746,  though  the  blistered  wing  is  characteristically  smaller  than  normal. 

not-rudimentary  female  which  had  in  each  wing  a  small  vesicle  in  the 
region  of  the  fifth  longitudinal  vein  just  beyond  its  junction  with  the 
posterior  cross- vein.     This  female  was  bred  to  a  wild-type  brother  and 

'MacDowell  ('15)published  bristle  counts  on  this  stock  under  its  earlier  name  of  "half-balloon." 


156 


THE    SECOND-CHROMOSOME    GROUP 


gave  only  wild-type  sons  and  daughters,  from  which  it  was  concluded 
that  the  character  was  recessive  and  non-sex-Unked.  The  F2  genera- 
tion gave  only  a  few  blistered  (about  1  in  10),  and  these  were  nearly 
all  females.  By  mating  together  the  blistered  individuals  in  pairs  a 
stock  was  obtained  which  must  have  been  genetically  homozygous  for 
blistered,  although  only  about  half  of  the  females  and  about  a  quarter 
of  the  males  showed  the  character.  It  had  been  noticed  that  the  size 
of  the  vesicle  varied  from  a  very  minute  bubble  to  one  which  covered 
over  half  the  area  of  the  wing,  and  that  there  was  not  a  very  close 
correspondence  between  the  two  wings;  frequently  the  bUster  would 
appear  in  only  one  of  the  two  wings.  A  closer  inspection  showed  that 
the  wings  which  did  not  show  a  vesicle  had  a  small  plexus  of  veins 
in  the  region  occupied  by  the  vesicle  (figs.  74  a  and  b),  and  it  was  found 
that  the  flies  could  be  quite  readily  classified  by  this  character,  irre- 
spective of  whether  they  showed  the  bUster  or  not.  At  the  same 
time  the  results  given  by  breeding  from  these  abnormally  veined  flies 
showed  that  the  venation  and  the  blistering  were  both  products  of 
the  same  gene.  A  third  manifestation  of  this  gene  is  a  sharp  bend  in 
the  distal  end  of  the  fourth  longitudinal  vein  (shown  in  text-figure  74,a). 

Table  18. — Pi  mating,  curved  cf  X  blistered  9  ;  ^1  mating, 
mid-type  99-}-  mid-type  cf  cT . 


Apr.  30. 
1912. 

Wild- 
type. 

Curved. 

Blistered. 

Curved 
blistered. 

B  12a 

B12b.... 
B12c 

Total 

81 
62 

58 

18 
25 
12 

23 

27 

6 

0 
0 
0 

201 

55 

56 

0 

THE  CHROMOSOME  OF  BLISTERED. 

Little  was  done  with  blistered,  aside  from  getting  the  pure  stock 
just  described,  until  the  discovery  that  black  and  curved  were  in  the 
same  chromosome  gave  a  sharp  impetus  to  further  study  of  autosomal 
linkage.  Shortly  thereafter  (April  3,  1912)  blistered  was  crossed  to 
curved  and  three  F2  cultures  were  raised  (table  18).  No  curved- 
blistered  flies  were  found  in  the  F2.  The  numbers  given  in  table  18 
represent  only  the  first  counts  from  each  of  these  three  cultures,  and  for 
this  reason  the  number  of  wild-type  flies,  which  are  the  first  to  hatch, 
is  abnormally  high.  No  further  records  were  made  of  the  F2  offspring, 
because  of  the  suspicion  that  blistered  might  not  be  distinguishable 
in  curved  flies,  and  that  the  absence  of  the  double  recessive  might  be 
due  to  inhibition  or  masking  instead  of  the  supposed  linkage.  Never- 
theless, all  the  F2  flies  were  examined  in  the  hope  of  finding  a  double 


OF   MUTANT   CHARACTERS. 


157 


recessive.  When  none  was  found  the  experiment  was  discontinued, 
since  it  was  thought  that  the  chances  of  finding  a  double  were  as  good 
in  F2  as  in  any  subsequent  generation — an  attitude  excusable  at  I  kit 
time,  before  the  fact  of  no-crossing-over  in  the  male  had  yet  been 
discovered. 

Table  19. — Pi,  blistered    9    X   pink  cf;  Fi  wild-type    9    and  cT. 


Auk.  10, 
1913. 

Wild 
type. 

Blistered. 

Pink. 

Pink 
blistered. 

M  52 

M  53 

Total 

157 
146 

60 
45 

58 
54 

25 
13 

303 

105 

112 

38 

Table  20.- 

—Pi,  blistered 

9     X 

black 

&. 

Oct.  23, 
1913. 

Wild-type  9. 

Wild-type  cf . 

Free-vein  9- 

Free-vein  cf. 

II  99 

27 

24 

48 

4 

B.C.,  Fi  free-vein  d"   X  black  9  • 

Nov.  23, 
1913. 

Non-cro8s-overs. 

Cross-overs. 

Black. 

Free-vein. 

Black  free-vein. 

Wild-type. 

9 

& 

9 

& 

9 

& 

9 

d^ 

II  111.... 
II  133.... 
II  134.... 
II  146.... 

Total 

86 
25 
51 
17 

87 
20 
45 
25 

60 
27 
33 
25 

16 

9 

15 

24 

2 
2 

1 

30 

10 

18 

2 

70 

19 

27 

9 

179 

177 

145 

64 

4 

1 

60 

135 

B.C.,  Fi  free-vein  9    X  black  cT.     (Nov.  4,  1913.) 

II  102.... 
II  109.... 
II  132.... 
II  144... 

Total 

67 
44 
39 
20 

74 
59 
62 
16 

32 

29 

32 

3 

10 
11 

8 
6 

21 

34 

16 

6 

5 

8 
1 
2 

32 
49 
49 
25 

63 
56 
61 
25 

170 

211 

96 

35 

77 

16 

155 

205 

The  tests  on  the  linkage  of  blistered  were  taken  up  again  after  the 
discovery  of  no-crossing- over  in  the  male  had  made  it  most  probable  that 
the  absence  of  the  double  recessive  curved  blistered  was  due  to  the 
genes  being  in  the  same  chromosome  rather  than  to  a  masking  effect  of 
curved.  At  this  time  (July  1913)  it  was  important  that  any  autosomal 
mutant  be  tested  as  to  its  linkage  with  both  the  second  and  the  third 
chromosomes,  and,  indeed,  it  was  by  the  uniform  results  of  many  such 
tests  that  convincing  proof  was  secured  that  the  second  and  third 


158  THE    SECOND-CHROMOSOME    GROUP 

chromosomes  are  independent  in  heredity.  Accordingly,  blistered  was 
mated  to  pink  as  the  tj^pical  third-chromosome  mutant.  The  F2  from 
this  cross  (table  19)  gave  a  9  :  3  :  3  : 1  ratio,  as  expected,  which  con- 
firmed the  view  that  bhstered  is  not  in  the  third  chromosome. 

Blistered  was  also  mated  to  black  as  a  representative  of  the  second 
chromosome;  curved  was  avoided,  since  it  was  planned  to  continue 
this  line  and  there  still  lingered  some  fear  of  the  masking  effect  of 
curved  on  blistered. 

THE  SEMI-DOMINANCE  OF  BLISTERED— FREE-VEIN. 

"WTien  the  Fi  flies  from  the  cross  of  blistered  to  black  (table  20)  began 
to  hatch,  it  was  noticed  (October  23,  1913)  that  nearly  two-thirds  of 
the  females  and  a  few  of  the  males  showed  a  small  section  of  vein 
lying  free  in  the  third  posterior  cell  and  parallel  to  the  fifth  longitudinal 
vein.  The  length  of  this  extra  vein  was  oftenest  about  two-thirds 
the  length  of  the  posterior  cross- vein,  but  it  varies  to  a  minute  dot. 
Flies  often  showed  it  in  only  one  wing.  This  character,  while  it  is  very 
irregular  in  occurrence,  is  very  easy  to  classify,  since  the  vein  is  clear 
and  sharp.  The  work  done  with  this  character  is  therefore  exact  and 
accurate,  without  the  approximations  and  close  decisions  that  are 
required  in  working,  for  example,  with  variable  colors  of  slight  average 
difference.  It  was  guessed  that  this  free  vein  occurring  in  Fi  was  due 
to  the  action  of  the  blistered  gene,  which  thus  shows  an  irregular  and 
partial  dominance.  If  this  were  true  it  should  be  possible  to  work 
with  blistered  as  a  dominant,  though  only  those  flies  which  actually 
show  the  character  can  be  used  in  calculations;  many  of  the  others, 
while  somatically  normal,  belong  genetically  with  those  showing  the 
free  vein.  Accordingly,  the  Fi  males  with  the  free  vein  were  back- 
crossed  to  black  females,  with  the  expectation  that  if  the  gene  for  the 
free  vein  (bhstered)  were  in  the  second  chromosome  all  of  the  off- 
spring would  be  either  black  or  free-veined,  there  being  no  crossing- 
over  in  the  male.  The  result  showed  that  the  gene  was  in  the  second 
chromosome  (table  20),  for  the  flies  which  were  extra- veined  were 
nearly  all  not-black.  There  were  5  black  flies  which  showed  a  slight 
development  of  an  extra  vein,  but  these  veins  were  probably  due  to 
other  causes,  since  2  of  the  flies  when  tested  gave  81  and  93  offspring, 
respectively,  none  of  which  showed  a  trace  of  the  free- vein  character. 
While  all  of  the  not-black  flies  must  have  been  of  the  same  consti- 
tution— i.  e.,  heterozygous  for  the  free- vein  gene — only  53  per  cent  of 
them  showed  the  extra  vein. 

At  the  same  time  that  the  Fi  free-veined  males  were  back-crossed, 
some  of  the  similar  females  were  likewise  back-crossed  (table  20). 
Since  in  the  female  there  is  crossing-over,  this  experiment  should  show 
the  amount  of  crossing-over  between  black,  whose  position  is  well 
known,  and  the  gene  for  the  free- vein ;  that  is,  we  should  obtain  one  of 


OF   MUTANT   CHARACTERS. 


159 


the  two  distances  required  to  determine  approximately  the  position 
of|the  gene  for  free-vein.  As  in  the  previous  experiment,  only  those 
flies  which  actually  show  the  free-vein  (about  a  quarter  of  the  whole 
number)  can  be  used  in  the  calculation.  As  shown  in  the  last  section 
of  table  20,  there  were  224  flies  with  the  free  vein,  of  which  93  or  41.5 
per'cent  were  cross-overs.  When  double  crossing-over  is  taken  into 
account,  this  value  indicates  that  the  gene  is  very  far  away  from  black 
in  the  second  chromosome,  probably  50  or  more  units  away.  At  this 
time  it  was  known  that  the  dominant  mutant  streak  was  in  the  left  end 

Table  21. — Pi,  free-vein  cf  X  streak  9  ;  B.C.,  Fi  streak  free-vein  9  X  loild  cf. 


Feb.  23, 
1914. 

Non-cross-overs. 

Cros3-o^•p^3. 

Streak. 

Free-vein. 

Streak 
free-vein. 

Wild-type. 

69 

19  9.      20  o^. 

5  9.        1  cT. 

4  9.      1  <f. 

15  9.     16  d^. 

Table  22- 

—Pi,  free-vein 

9   X  speck  (S 

1 

Feb.  9. 
1914. 

Wild-type  9- 

Wild-type  cT. 

Free-vein  9  • 

Free-vein  cT. 

19 
20 

Total 

42 
18 

37 
27 

14 
15 

7 
13 

60 

64 

29 

20 

B.C.,  Fi  free-vein  9 

X  speck  cf  ■ 

Feb.  27, 
1914. 

Non-cross-over-j. 

Cross-overs. 

Free-vein. 

Speck. 

Free-vein  speck. 

Wild-type. 

72 
73 

Total 

12 
10 

9 
2 

46 
41 

42 
31 

1 
1 

1 

39 
26 

32 

28 

22 

11 

87 

73 

2 

1 

65 

60 

of  the  chromosome,  and  while  its  portion  was  not  accurately  known, 
it  was  at  least  30  units  to  the  left  of  black.  The  right  end  of  the  chro- 
mosome was  well  mapped  for  at  least  50  units,  so  that  while  the  gene 
for  the  free  vein  might  possibly  be  in  either  end,  it  was  more  probably 
in  the  right  end.  Both  of  these  possibilities  were  tested.  A  free- 
veined  male  was  mated  to  a  streak  female,  and  one  of  the  Fi  streak  free- 
veined  females  was  out-crossed  to  a  wild  male,  which  corresponds  in 
this  case  to  the  double  recessive.  Five  of  the  eleven  free-veined  flies 
were  streaked  (table  21),  which  free  crossing-over  means  that  the  free- 
vein  gene  is  not  in  the  left  end  of  the  chromosome  and  is  therefore  in 
the  right  end.  This  fact  was  shown  directly  by  the  test  with  speck, 
whose  locus  is  in  the  right  end  of  the  chromosome.     A  free- veined 


160  THE    SECOND-CHROMOSOME    GROUP 

female  (from  II 144,  table  20)  was  outcrossed  to  a  speck  male,  with  the 
regular  result  shown  in  table  22.  Two  of  the  Fi  free-veined  females 
were  back-crossed  to  speck  males  (table  22).  There  were  36  free- 
veined  flies,  of  which  only  3  or  8.3  per  cent  were  speck,  i.  e.,  cross-overs. 
Since  bkick  gives  about  48  per  cent  of  apparent  crossing-over  with 
speck  and  only  41.5  with  free- vein,  it  is  probable  that  the  gene  for 
free-vein  hes  to  the  left  of  speck  rather  than  to  the  right.  Certain 
more  recent  work  makes  it  probable  that  the  locus  of  blistered  is  con- 
siderably nearer  to  speck,  perhaps  only  two  units  away,  or  at  103  =t . 

JAUNTY  0). 

^  (Plate  7,  figure  3.) 

DISCOVERY  AND  STOCK  OF  JAUNTY. 

Shortly  after  the  discovery  of  ''blistered,"  the  wing  mutation 
"jaunty"  was  found  by  Bridges  (December  11,  1911)  in  the  same 
stock,  rudimentary,  in  which  blistered  had  appeared.  On  account  of 
the  low  productivity  of  rudimentary  females,  the  rudimentary  stock 
was  being  carried  on  by  continually  back-crossing  rudimentary  males 
to  heterozygous  females.  When  this  method  is  used,  only  half  of  the 
flies  in  each  generation  are  expected  to  show  the  character  rudimentary, 
the  other  half  being  wild-type.  The  first  jaunty  seen  was  one  of  the 
not-rudimentary  females  (notebook  A,  p.  34)  whose  wings  turned  up 
"jauntily  "  at  their  tips.  Next  day  a  jaunty  male  appeared  in  the  same 
culture.  The  fact  that  the  character  had  appeared  in  both  sexes 
suggested  that  it  was  not  sex-linked  unless  dominant.  These  two 
jaunties  were  bred  to  wild-type  flies  of  the  same  culture  and  in  Fi  gave 
offspring  none  of  which  showed  a  trace  of  jauntiness.  That  is,  jaunty 
was  recessive  and  autosomal  (not  sex-linked).  Jaunty  reappeared  in 
F2  as  approximately  a  quarter  of  the  flies  of  both  sexes,  but  no  accu- 
rate counts  were  made  because  the  presence  of  another  wing-charac- 
ter, rudimentary,  tended  to  make  the  classification  difficult.  To  mate 
mutants  to  flies  of  the  stock  in  which  they  first  appear  is  poor  policy 
because  of  this  presence  in  succeeding  generations  of  characters  which 
are  more  apt  to  be  hindrances  than  helps.  In  this  case  it  required 
continued  selection  of  the  jaunty  not-rudimentary  individuals  to 
establish  a  stock  that  was  pure  for  jaunty  and  entirely  free  from 
rudimentary. 

DESCRIPTION  OF  JAUNTY. 

The  wings  of  jaunty  flies  are  turned  upward  at  their  tips,  the  curva- 
ture usually  involving  only  the  terminal  third  or  half  of  the  wing, 
though  sometimes  the  basal  region  is  also  more  or  less  curved.  The 
amount  of  curvature  is  rarely  great  enough  so  that  the  tip  is  at  right 
angles  to  its  normal  position,  the  usual  curvature  being  through  30  to 


OF    MUTANT    CHARACTERS.  1(U 

70  degrees.  It  is  this  typical  curvature  of  the  wing  that  is  used  in 
classification,  though,  as  is  usually  the  case  with  mutations,  there  are 
present  various  associated  or  accessory  characteristics  which  are  of 
value,  but  which  in  this  case  must  not  be  relied  on  over  much.  Thus, 
the  upper  lamina  of  the  wing  is  frequently  corrugated  transversely, 
which  is  probably  the  cause  of  the  curvature,  though  it  may  be  the 
result.  The  '^nner"  side  of  the  wing  (posterior  margin)  is  often  more 
strongly  curved  than  the  "outer,"  and  in  these  cases  the  tips  of  the 
wing  have  a  sHght  obhque  slant  "outward."  The  jaunty  wings  have 
a  tendency  to  be  spread  farther  apart  than  normal,  though  the  amount 
of  divergence  is  slight.  In  color  the  wings  are  a  clear  gray,  slightly 
darker  than  normal,  and  are  of  strong,  thick  texture,  not  flimsy,  as  in 
certain  other  wing  mutations.  The  body-color  also  is  probably  a  trifle 
darker  than  normal.  All  of  these  accessory  characters  are  so  slight 
that  they  would  ordinarily  be  unnoticed. 

A  "MUTATING  PERIOD"  FOR  JAUNTY. 

Soon  after  the  discovery  of  jaunty,  a  character  which  seemed  to  be 
the  same  as  jaunty  was  found  (May  1912)  by  Morgan  to  be  present  in 
the  F2  of  a  cross  of  yellow  abnormal  to  white.  In  rapid  succession 
(May,  June,  July,  1912)  jaunty  or  jaunty-like  characters  were  dis- 
covered in  some  half  dozen  stocks  or  experiments,  so  that  the  idea  of  a 
"mutating  period"  for  jaunty  became  current.  It  is  possible  that 
the  jaunty  mutation  did  occur  on  more  than  one  occasion;  certainly  we 
were  unable  to  trace  any  recent  or  probable  connection  between  three 
of  these  appearances  of  jaunty,  namely,  the  two  just  given  and  a  case 
which  appeared  in  the  crosses  by  Bridges  of  purple  vestigial  to  wild. 
There  are  plenty  of  proved  cases  in  which  a  mutant  character  (or  an 
undistinguished  allelomorph)  has  appeared  on  a  second  or  third  occa- 
sion, and  there  is  no  a  priori  reason  why  these  several  mutations  might 
not  occur  at  about  the  same  time.  But  there  are  several  points  to  be 
guarded  against  before  accepting  any  supposed  recurrence  of  a  muta- 
tion as  genuine.  For  example,  it  is  surprising  through  how  many  gen- 
erations a  recessive  will  persist  in  a  mass  stock  even  when  the  character 
is  poorly  viable  and  is  selected  against  in  a  rough  fashion.  Thus,  the 
wing  mutation  "spread"  occasionally  crops  out  in  the  black-plexus 
stock  where  it  has  been  carried  along  "under  the  surface"  for  three 
years,  some  75  generations.  Any  cross  made  with  the  black-plexus 
stock  is  liable  to  transmit  the  spread  also,  so  that  a  recent  case  of 
spread  reappearance  was  finally  run  to  earth  as  coming  from  a  black- 
plexus  cross  made  some  six  months  pre\'iously.  Cases  like  this  are 
all  too  frequent  and  emphasize  the  value  of  strict  pedigrees  and  of 
"cleaned  up"  stocks.  Another  point  is  the  pyschological  one  of 
recognition.  One  can  fail  to  see  a  mutation  which  has  been  contin- 
ually present  in  flies  examined  for  some  generations,  and  which  is  so 


162 


THE    SECOND-CHROMOSOME    GROUP 


distinct  that  when  attention  has  been  forcibly  drawn  to  it  one  wonders 
how  it  is  possible  to  have  been  so  blind.  Thus,  for  example,  the  type 
** jaunty"  having  been  recognized,  suddenly  in  certain  other  stocks 
wings  that  have  been  passed  over  as  ''imperfectly  unfolded"  or  only 
vaguely  recognized  as  "queer"  are  seen  to  be  sharply  characterized 
"  jaunties."  Again,  of  the  20  or  so  mutations  previously  found  it  had 
happened  that  only  2,  rudimentary  and  truncate,  bore  much  resem- 
blance to  each  other,  and  we  were  then  far  less  critical  than  now  as  to 
whether  a  new  jaunty-like  mutation  was  actually  jaunty  or  only  a 
mimic.  To  the  "genus"  jaunty  there  are  now  at  least  four  well 
recognized  "species" — jaunty,  jaunty  X  (sex-linked),  curled,  and  Cali- 
fornia curled.  A  similar  mutating  period  for  purple  resulted  in  iso- 
lation of  maroon  as  a  distinct  but  very  close  mimic  and  the  "mutating 
period  of  arc"  brought  forth  arch,  bow,  arc2,  depressed,  and  even  other 
types  distinct  in  inheritance  though  similar  in  appearance  ('arcoids'). 

Table  23. — Pi,  jaunty  9  X  black  cf;  Fi  wild-type  99  -f-  /^i  wild-type  cfcf . 


Dec.  16, 
1912. 

Wild- 
type. 

Black. 

Jaunty. 

Black 

jaunty. 

117 

546 

283 

249 

0 

Table  24.— Pj,  jaunty  cfcf  Xcurved  99;  Fi  wild-type  99  +  Fi 

wild-type  <^  cf . 


Dec.  7 
1912. 

Wild- 
type. 

Jaunty. 

Curved. 

Jaunty 
curved. 

C164.... 

531 

216 

2S5 

0 

CHROMOSOME  AND  LOCUS  OF  JAUNTY. 

The  fact  that  the  gene  for  jaunty  is  carried  by  the  "second"  chro- 
mosome appeared  in  the  Fg  from  the  cross  of  a  jaunty  female  to  a  black 
male,  when  a  mass-culture  of  the  Fi  wild-type  miales  and  females  gave 
a  2  : 1  : 1  : 0  F2  ratio  (table  23).  The  F2  jaunty  flies  were  mated  to 
the  F2  blacks,  this  being  considered  the  most  advantageous  method  of 
working  for  the  double  recessive  black  jaunty.  In  F3  only  wild-type 
flies  appeared.  The  blacks  or  jaunties,  which  would  have  indicated 
crossing-over  (in  the  Fi  female)  between  black  and  jaunty,  and  which, 
indeed,  would  have  given  black-jaunty  stock  in  F4,  did  not  appear. 
Accordingly  these  wild-type  flies,  F3  offspring,  which  were  like  the 
original  Fi,  were  inbred  to  give  a  new  F2,  and  many  more  black  X  jaunty 
tests  were  made.  Again  (F5)  no  blacks  or  jaunties  appeared,  and  this 
indicated  that  the  loci  of  black  and  jaunty  are  very  close  together  in 
the  chromosome.  On  several  occasions  attempts  were  made  by  the 
above  method  to  get  the  double  recessive.     By  a  calculation  from  the 


OF   MUTANT    CHARACTERS.  163 

number  of  flies  tested  and  proved  to  be  non-cross-overs,  it  was  shown 
that  these  loci  were  probably  within  2  or  3  units  of  each  other.  I^ter 
a  more  refined  method  was  used,  whereby  only  such  flies  were  tested 
as  were  known  to  be  cross-overs  very  close  to  black,  that  is,  between 
dachs  and  black  or  between  black  and  purple.  The  results  of  these 
tests  only  served  to  bring  out  more  clearly  that  the  locus  of  jaunty 
was  very  close  to  that  of  black. 

When  the  black  X  jaunty  cross  failed  to  give  the  double  recessive, 
a  more  roundabout  method  was  started  by  crossing  jaunty  to  curved. 
The  F2  jaunties  (table  24)  were  inbred  instead  of  being  crossed  to  the 
F2  curved.  This  was  to  avoid  possible  doubt  as  to  the  double  form 
being  separable  from  curved.  Any  curved  flies  descended  from  the 
inbred  F2  jaunties  must  be  the  double  recessive  form  jaunty  curved. 
Fortunately,  jaunty  curved  flies  appeared  in  F3  and  a  stock  was  made 
up.  The  wings  of  the  jaunty  curved  flies  were  easily  classified  as 
curved,  and,  surprisingly  enough,  the  jauntiness  was  usually  detectable 
in  the  wing-tips.  The  intended  experiments  were  not  carried  out 
with  this  stock,  but  Muller  (Muller,  1916)  used  it  in  building  up  the 
multiple  heterozygotes  which  he  tested.  The  tests  of  Muller  furnished 
462  flies,  of  which  possibly  one  was  a  cross-over  between  black  and 
jaunty.  If  this  questioned  cross-over  were  genuine,  jaunty  would  be 
mapped  to  the  right  of  black  and  0.2  unit  away.  If  the  apparent  cross- 
over were  due  to  error,  then  we  are  only  certain  that  jaunty  is  excep- 
tionally close  to  black. 

A  large  series  of  crosses  between  jaunty  and  the  third-chromosome 
mutant  pink,  carried  out  by  a  graduate  student,  Mrs.  Binkley,  gave 
most  interesting  and  puzzling  results,  the  data  for  which  was  unfor- 
tunately lost  with  the  second-chromosome  summaries.  As  we  recall  the 
case,  the  F2  ratios  were  more  nearly  4:2:2:1  than  9:3:3:1.  The 
back-crosses  likewise  gave  aberrant  ratios  which  we  could  not  explain 
as  due  to  viability  effects  and  which  were  not  due  to  linkage  disturb- 
ances in  the  relation  of  jaunty  and  pink,  since  the  back-cross  tests  of 
Fi  males  and  Fi  females  gave  like  results,  in  which  the  percentage  of 
recombination  was  approximately  50,  as  expected.  Besides  these 
peculiarities  of  the  ratios  there  was  a  curious  appearance  of  white- 
eyed  flies  which  in  inheritance  reminded  us  somewhat  of  the  case  of 
"whiting,"  an  eosin  modifier  worked  out  by  Bridges,  but  which  was 
far  more  elusive  in  the  manner  of  the  alternate  appearance  and  dis- 
appearance of  white  and  in  the  relation  of  pink  to  the  case. 

VALUATION  OF  JAUNTY. 

Though  jaunty  is  easily  separable  from  wild-type  and  is  of  good 
viability  and  behavior,  it  is  not  much  used.  The  main  drawback  is 
the  closeness  of  its  locus  to  another  locus  already  satisfactorily  filled 
by  black.     This  region  of   the  chromosome   could   be   represented 


164 


THE    SECOND-CHROMOSOME   GROUP 


equally  well  by  jaunty  or  by  black,  but  black  continues  to  be  chosen, 
because  of  its  greater  prestige,  because  black  already  exists  in  many  use- 
ful combinations  and  multiple  stocks,  while  jaunty  is  not  combined  with 
other  useful  characters,  and  because  black  has  at  present  less  masking 
effect  than  jaunty.  The  wing-mutations  of  the  second  chromosome  are 
rekitively  numerous  and  tend  to  mask  each  other's  effects.  Generally, 
therefore,  two  wing-characters  are  not  used  simultaneoulsy,  and  the 
choice  falls  on  the  one  having  the  locus  best  adapted  for  the  particular 
experiment.  If  jaunty  were  in  the  neighborhood  of  streak  or  in  any  of 
the  long  empty  regions  of  the  second  chromosome  it  would  be  consid- 
ered a  mutation  of  first  rank. 


CURVED  (c). 

(Text-figure  75.) 

DISCOVERY  AND  STOCK. 

A  third  mutation  in  the  rudimentary  stock,  curved  wings,  was  found 
by  Bridges  December  24,  1911  (notebook  A,  p.  43).  This  mutation 
appeared  in  both  males  and  females  and  both  as  rudimentary  and  as 
not-rudimentary  individuals  (fig.  75),  from  which  facts  it  was  concluded 
that  the  mutation  was  probably  not  sex-linked.  The  not-rudimentary 
curved  males  and  females  were  mated  together  and  produced  in  the 
next  generation  a  stock  about  80  per  cent  of  which  was  curved;  the 
20  per  cent  of  not-curved  flies  was  the  result  of  non- virgin  mothers. 

Virgin  not-rudimentary  curved  females  were  mated  in  pairs  to 
similar  males,  and  all  of  these  pairs  produced  pure  stock  of  curved. 
Furthermore,  about  half  of  the  pairs  gave  no  rudimentary  sons,  and 
these  cultures,  known  to  be  entirely  free  from  rudimentary,  were  used 
as  the  permanent  stock  of  the  mutation. 

DESCRIPTION  OF  CURVED. 

The  most  characteristic  feature  of  the  mutation ''  curved  "  is  perhaps 
the  thin  texture  of  the  wing  and  its  accompanjdng  slight  but  charac- 
teri'stic  crinkhness  like  waxed  paper.  More  striking  than  the  texture, 
though  perhaps  a  result  of  it,  is  the  strong  downward  curve  of  the  wing. 
The  curved  wings  are  generally  held  out  at  a  wide  angle  (60°)  from 
the  body  and  are  elevated  (30°  to  60°).  The  pose  and  curvature  of 
the  wings  are  quite  bird-like,  and  the  first  name  of  the  mutation  was 
"gull."  The  divergence  of  the  wings,  as  in  all  other  mutants  possess- 
ing such  a  characteristic,  is  the  first  index  of  the  mutation  to  catch  the 
eye  when  the  flies  are  drawn  out  in  a  windrow  for  separations.  In  a 
few  of  the  flies  both  the  elevation  and  the  divergence  of  the  wings  are 
sHght,  and  in  these  cases  the  curvature  and  the  texture  of  the  wings 
are  used  as  indexes.    In  spite  of  the  thin  texture  of  the  wing  and  the 


OF    MUTANT   CHARACTERS. 


1G5 


Text-figure  75. — Curved  wings.     75a,  curved  aa  seen  from  above;  756,  as  seen  from  the  aide 
and  above.     (Fig.  75,  b,  shows  speck  also,  having  been  drawn  from  a  purple  curved  speck  fly.) 


166 


THE   SECOND-CHROMOSOME   GROUP 


wide  angle  at  which  it  is  held,  the  curved  wing  seldom  becomes  bedrag- 
gled, and  the  flies  are  very  free  from  the  tendency  to  become  stuck  in 
the  food  or  to  be  drowned.  As  far  as  we  have  observed,  the  wings  are 
the  only  part  affected  by  the  curved  mutation. 

CHROMOSOME  OF  CURVED. 

The  first  hnkage  in  Drosophila  that  did  not  involve  the  X  chromo- 
some was  thut  observed  by  Bridges  (March  1912)  between  black  and 
curved  (Bridges  and  Sturtevant,  1914).  In  the  F2  generation  of  a 
cross  of  black  to  curved  no  black-curved  flies  appeared.  This  case 
was  interpreted  as  one  in  which  the  hnkage  was  of  such  a  strong 
order  that  no  crossing-over  had  taken  place.  On  the  basis  of  this 
linkage  it  was  concluded  tha,t  curved  was  in  the  same  chromosome  as 
black,  that  is,  in  a  "second  chromosome."  A  systematic  search  for 
hnkage  between  the  other  known  non-sex-linked  genes  in  Drosophila 
was  undertaken,  and  a  similar  relation,  "repulsion,"  was  studied  in 
the  case  of  black  and  vestigial  (Morgan  and  Lynch,  1912).  Further 
work  by  Morgan  in  the  case  of  black  and  vestigial  showed  that  the 
non-appearance  of  the  double  recessive,  where  two  second-chromo- 
some recessives  entered  the  Fi  from  opposite  parents,  could  be  ex- 
plained on  the  basis  of  lack  of  crossing-over  in  the  male.  It  was  soon 
shown  that  this  same  explanation  applied  in  the  case  of  black  curved, 
and  that  in  the  female  there  is  considerable  crossing-over  between  these 
two  loci. 

LOCUS  OF  CURVED. 

In  order  to  obtain  stock  of  the  double  recessive,  the  black-curved 
cross  was  repeated,  and  some  of  the  F2  blacks  were  mated  in  mass- 
cultures  to  the  F2  curved  flies  of  the  other  sex.     If  crossing-over  were 

taking  place  in  the  Fi  female  ( —r >  |  ) , 

F2  blacks  should  be  heterozygous  for  curved  ( -r )  and  a  corre 

sponding  few  of  the  curves  should  be  heterozygous  for  black  ( 


,  a  few  of  these 


\  c 


y 


The  appearance  in  F3  of  a  few  black  flies  (-r — —j  showed  that  at 

least  one  of  the  F2  curved  flies  had  been  the  result  of  crossing-over. 
By  inbreeding  these  F3  blacks,  black  curved  flies  (25  per  cent)  were 
secured  in  F4. 

That  the  absence  of  black  curved  flies  in  F2  was  really  due  to  lack  of 
crossing-over  in  the  male  was  shown  by  the  results  of  the  back-cross 
tests  carried  out  upon  double  heterozygous  males  as  compared  with 
like  tests  of  the  females.  In  the  tests  of  the  males  no  cross-overs 
appeared  in  a  total  of  1,066  flies,  while  in  the  tests  of  the  females  1,717 


OF   MUTANT    CHARACTERS. 


107 


Table  25. — Summary  of  cross-over  data  invohing  curved  and  other  second- 
chromosome  loci. 


Loci. 


Star  curved .  . 

Streak  curved. 

Dacha  curved. 
Black  curved . 


Purple  curved , 


Lethal    Ila 
curved 


Vestigial 
cun'ed. 


;;urved  speck. 


urved  balloon 


Total. 


6,766 
13,104 


19,870 


1,807 
462 


2,269 


462 


7,419 

260 

253 

402 

3,934 
223 

462 
36,622 

13,104 


62,679 


3,934 

1,807 

462 

952 

36,622 

6,766 

593 


51 

,136 

249 

856 
402 
462 

1 

,720 

1,007 

223 

462 
952 

6,766 
632 


10,042 


462 


Cross- 
overs. 


3,164 
5,959 


9,123 


745 
178 


923 


145 


1,717 

69 

66 

120 

839 
63 

106 

8,598 

2,659 


14,237 


711 

375 

90 

182 

7,222 

1,508 

117 


10,205 


22 


75 
32 

34 


141 


262 

71 

150 
266 

2,062 
226 


3,037 


150 


Per- 
cent. 


46.8 
44,4 


45 

9 

41 

38 

2 
5 

40 

7 

31 

4 

23.1 

25.5 
26.1 
29.9 

21.3 

28.2 

22.9 
23.4 

20.3 


22.7 


18.1 
20.7 
19.5 
19.1 
19.7 

22.3 

19.7 


19.9 


8.7 


8.8 
8.0 
7.4 


8.2 


26.0 

31.8 

32.5 
27.9 

30.5 
35.7 


30.2 


32.5 


Date. 


July  11,  1915 
Dec.  15,  1915 

Nov.  6,  1913 
May  — .  1914 

May  — ,  1914 
Jan.   13.  1913 

Jan.   13,  1913 

Jan.   13,  1913 

June    8,  1913 

Aug.  24,  1913 
Oct.   16,  1913 

May  — ,  1914 
Jan.     5,  1915 

Dec.  13,  1915 

Aug.  24,  1913 
Nov.  6,  1913 
May  — ,  1914 
Aug.  24,  1914 
Jan.    8,  1915 

July  11,  1915 

Feb.    8,  1916 


Dec.  21,  1915 

Mar.  14,  1913 
June  8,  1913 
May  — ,  1914 


Mar.  10,  1913 

Oct.    16,  1913 

May  — .  1914 
Aug.  24,  1914 

July  11,  1915 
Feb.    8,  1916 

May  — ,  1914 


By- 


Bridges  . . 
Plough .  .  . 


Bridges . 
Muller . 


Muller 

B.  &  Strt. .  . 

Do. 

Do. 

Sturtevant . 

Bridges .... 
Sturtevant . 

Muller 

Plough 

Plough 

Bridges . . .  . 
Do. 

Muller 

Bridges .  . . . 
Plough .  .  .  . 

Bridges . . .  . 

Do. 


Bridges . . .  . 

Sturtevant 
Do. 

Muller 


Sturtevant 

Do. 

Muller. . . . 
Bridges ... 

Do. 

Do. 

Muller 


Reference. 


S'; 


S' 


Pr  c  Sp 


B.C.  Ista;  18.}6-'94. 


J.  E.  Z..  '17, 


B.(.".  controlH. 


S't;  S'  balanced  B.C.;  II  10;}-124. 
Am.  Nat.,  1916,  p.  422. 

Am.  Nat.,  1916,  p.  422. 

Biol.  Bull.,  1914.  p.  209;  6  c  and 

b 

—  B.C. 

c 

Biol.  Bull.,  1914.  p.  JOS;  b  c  F,. 

Biol.  Bull.,'l914.  p.  212;  —  B.C. 

c 

Zeit.    f.  i.  A.  u.   v.,   '15,   p.  247; 
*,  bvgc  B.C. 

Pr:  b  Pr  c  B.C.  1st.'*;  II  .W-II  88. 
IZeit.    f.  i.  A.   u.   V.;   '15,   p.  247; 

bc8p  B.C. 
Am.  Nat.,  1916,  p.  422. 
J.  E.  Z.  1917,  h  Pr  c  B.C.  controla. 


J.  E.  Z.  1917, 


be 


B.C.  controlB. 


Pr.-  b  Pr  c  B.C.   lots;  II  58^1188. 

S't;  S'l  Pr  c  balanced  B.C. 

Am.  Nat.,  1916,  p.  422. 

sp;  PrC  Kp  B.C.;  452-508. 

J.  E.  Z.  '17,  b  PrC  B.C.  controls. 

.S" 
S';  B.C.  Ists;  1836- '94. 

Pr  C  Sp 

hi  a:  >>  Pr  c  Fi;  3203-'08. 


hia:  /;/oC  Fj; 2675, 2840;  '59,  '60,  '63 

Zcit.  f.  i.  \.  u.  v..  p.  245,  r,  c  B.C. 
Zeit.  f.  i.  A.  u.  v.,  p.  247,  r,  r  s,  B.C. 
Am.  Nat.,  1916,  p.  422. 


Zeit.    f.   i.   A.   u.   V.,   '15.   p.  245; 

c  Sp  B.C. 
Zeit.    f.   i.   A.    u.    v..    '15.    p.    247; 

be  KpB.V. 
Am.  Nat.,  1916.  p.  422. 
Sp;  Pr  c  8p  B.C.;  452-508. 

S' 

S': B.C..  l8t«.;  183&^'94. 

Pt  c  Kp 

lua:  Pr  r  "p  >'»:  3203- "08. 


Am.  Nut.,  1916.  p.  422. 


168 


THE    SECOND-CHROMOSOME    GROUP 


cross-overs  appeared  in  a  total  of  7,419  flies  (Bridges  and  Sturtevant, 
1914).  In  the  male  there  was  no  crossing-over  whatever,  while  in 
the  female  there  was  about  25  per  cent. 

The  direction  along  the  II  chromosome  from  black  to  curved  was 
called  "to  the  right,"  and  curved  was  therefore  mapped  at  a  locus  25 
units  to  the  right  of  black. 

The  position  of  curved  has  been  more  accurately  determined  by 
use  of  intermediate  loci  than  was  possible  from  the  rather  long  black 
curved  interval.  Thus  the  purple  curved  stock,  made  by  Bridges  in 
preparation  for  the  triple  back-cross  black  purple  curved,  was  used  by 
Mr.  W.  S.  Adkins  to  run  extensive  purple  curved  back-cross  tests. 
These  crosses,  the  data  for  which  are  not  yet  available,  gave  about  18 
per  cent  of  crossing-over  between  purple  and  curved,  which  agrees 
with  the  result  of  the  black  purple  curved  back-crosses.  Much  data 
has  since  been  collected  on  this  cross-over  value,  largely  incidental  to 
the  work  on  age  variation  by  Bridges  and  temperature  variation  by 
Plough.  A  total  of  51,136  flies  included  10,205  cross-overs  between 
purple  and  curved ;  the  observed  percentage  of  crossing-over  was  thus 
19.9.  It  is  possible  that  there  is  considerable  double  crossing-over 
within  this  region,  since  it  is  in  the  middle  of  the  chromosome,  where 
double  crossing-over  in  relation  to  map-distance  has  been  found  to  be 
extraordinarily  high.  If  a  coincidence  of  70  is  assumed,  the  corrected 
purple-curved  value  becomes  21.4  and  the  locus  of  purple  is  27.6  units 
to  the  right  of  bla-ck. 

The  locus  of  curved  was  also  referred  to  vestigial  by  Sturtevant,  who 
ran  vestigial  curved  and  black  vestigial  curved  back-crosses.  This 
method  has  great  advantages  in  mapping  the  locus  of  curved,  since 
vestigial  is  itself  accurately  mapped  in  relation  to  purple  and  is  an 
intermediate  base  between  purple  and  curved.  Only  the  not-vestigial 
back-cross  flies  can  be  used  in  the  calculation,  since  curved  vestigials 
can  not  be  distinguished  from  the  simple  vestigial  class.  Hence  the 
vestigial  curved  data  are  too  meager  as  yet  (1,720  flies)  to  be  used 
as  the  main  basis  of  the  location  of  curved. 

A  sumLmary  of  the  cross-over  data  involving  curved  and  other  second- 
chromosome  loci  is  given  in  table  25. 

VALUATION  OF  CURVED. 

Curved  is  in  all  respects  a  mutant  character  of  first  rank,  both  for 
student  use  and  in  special  experiments.  Its  separabiUty  from  the 
wild-type  is  both  eagy  and  accurate,  even  without  experience.  Its 
viability  is  excellent.  It  causes  no  trouble  through  liability  to  drown- 
ing or  miring,  which  might  have  been  expected  on  account  of  the 
strongly  divergent  wings.  Its  locus  is  the  outpost  of  the  central  body 
of  well-mapped  genes  and  it  is  therefore  the  base  of  reference  for  speck 
and  for  all  genes  near  the  right  end  of  the  chromosome. 


OF   MUTANT   CHARACTERS.  169 

PURPLE  (p.). 

(Plate  5,  figure  8.) 

ORIGIN  OF  PURPLE. 

In  a  stock  kept  in  the  stock-room  and  supposed  to  be  simply  vesti- 
gial, there  was  found,  February  20,  1912,  a  single  male  which  had  an 
eye-color  much  like  that  of  the  well-known  double  recessive  vermilion 
pink.  The  color  of  the  vermilion  pink  eye  is  about  that  of  the  pulp  of 
an  orange,  and  the  early  papers  accordingly  referred  to  this  double 
recessive  as  ''orange."  The  new  color  was  seen  to  differ  slightly  from 
vermilion  pink  in  that  it  Was  of  a  brilliant  ruby-like  transparency 
and  lacked  the  flocculent  or  slightly  cloudy  appearance  of  vermilion 
pink.  This  difference  seems  to  arise  partly  from  a  difference  in  the 
distribution  of  the  pigment.  In  vermihon  pink  the  pigment  looks  as 
though  it  were  mainly  in  the  spaces  between  the  radially  arranged 
ommatidia  with  a  clearer  zone  just  under  the  surface  of  the  eye.  One 
sees  in  the  vermilion  pink  eye  a  light  fleck  which  travels  over  the  eye 
as  it  is  turned.  This  seems  to  be  due  to  a  deficiency  of  pigment  in  the 
deeper  parts  of  the  eye  and  the  light  fleck  is  this  light  center  seen 
through  the  small  group  of  facets  whose  axes  are  in  hne  with  our  eye. 
The  pigment  in  the  case  of  the  new  eye-color  gave  the  appearance  one 
would  expect  if  it  were  uniformly  distributed  or  even  in  solution 
throughout  the  eye. 

INHERITANCE  OF  PURPLE. 

This  single  male  with  the  orange-like  eye-color  was  out-crossed  to  a 
wild  female,  and  in  Fi  gave  only  wild-type  males  and  females  (wild- 
type  9  32,  cf  33;  reference  No.,  B  1)  which  showed  that  the  color 
was  recessive.  In  F2  the  orange-like  color  reappeared,  but  in  addition 
the  sex-linked  eye-color  vermilion  emerged,  and  also  a  new  eye-color 
"purple"  which  appeared  equally  among  the  F2  females  and  males  and 
was  therefore  known  to  be  an  autosomal  (not  sex-linked)  character. 
It  was  now  evident  that  the  orange-like  color  resembled  the  old 
"orange"  (vermihon  pink)  genetically  as  well  as  somatically,  for  it 
was  proved  by  this  F2  to  be  a  double  recessive,  vermilion  purple,  in 
which  purple  corresponds  to  pink. 

It  seems  probable  that  the  two  eye-color  mutations,  vermihon  and 
purple,  present  in  the  male  first  found  were  not  of  simultaneous  or 
related  origin.  There  was  a  vague  rumor  that  the  vestigial  stock  had 
contained  vermihon  at  some  time  previous  to  this  discovery.  No 
vermihon  or  purple  was  found  in  it  subsequently,  however. 

DESCRIPTION  OF  PURPLE. 

The  eye-color  of  purple  flies  passes,  in  its  development,  through  an 
interesting  cycle  of  changes  closely  parallel  to  those  seen  in  the  ripen- 
ing of  a  sweet  cherry.     In  the  pupa  the  eye  is  at  first  colorless,  then  it 


170  THE   SECOND-CHROMOSOME    GROUP 

assumes  a  creamy  tone  which  in  turn  becomes  pinkish,  passing  pro- 
gressively through  a  j^ellowish  pink  to  pink  and  to  ruby.  When  the 
flies  hatch,  the  color  is  a  transparent  rather  deep  ruby.  This  color 
rapidly  deepens  to  garnet  and  then  passes  on  to  a  purplish  tone.  The 
typical  purple  color  at  its  maximum  development — in  flies  about  a 
day  old — while  retaining  much  of  its  transparency,  appears  darker  in 
tone  than  the  red  of  the  wild-type,  purple  being  the  first  of  such 
"dark"  eye-colors.  As  the  fly  becomes  older  this  "ripe- cherry"  color 
is  progressively  obscured,  apparently  by  an  increase  in  a  flocculent 
red  pigment,  hke  that  of  the  wild  fly.  The  eye-color  thus  becomes 
somewhat  lighter  than  red  again,  though  always  distinguishable  by  a 
lesser  opacity  and  by  a  light  "fleck"  in  place  of  the  hard  dark  fleck 
seen  in  the  wild  eye.  With  extreme  old  age  the  color  approaches  still 
closer  to  red,  but  does  not  become  strikingly  darker,  as  do  pink  and 
sepia,  for  example.  In  purples  of  the  same  age  fluctuations  in  color 
are  not  great.  Separations  are  easy  if  done,  as  usual,  while  the  flies 
are  mostly  under  2  days  old,  though  the  climax  in  the  development  of 
the  purplish  tone  offers  the  most  favorable  stage. 

THE  DIFFERENTIATION  OF  PURPLE  BY  VERMILION— DISPROPOR- 
TIONATE MODIFICATION. 

While  the  difference  between  the  color  produced  by  the  purple  gene 
and  the  color  produced  by  its  wild-type  allelomorph  (red)  is  distinct, 
it  is  neither  great  nor  striking,  since  in  tone  purple  is  first  slightly 
darker  and  later  somewhat  lighter  than  red.  However,  in  classifying 
the  eye-colors  in  F2  from  the  cross  of  vermihon  by  wild,  it  was  observed 
that  the  difference  between  vermihon  purple  and  vermihon  not- 
purple  was  not  only  constant  in  direction,  but  also  conspicuous  in 
extent.  The  separability  of  purple  versus  not-purple  is  favored  by 
the  presence  of  vermilion,  which  may  therefore  be  called  a  "differentia- 
tor" of  purple.  Regarded  in  the  converse  relation,  namely,  the  effect 
of  purple  on  vermilion  rather  than  the  effect  of  vermilion  on  purple, 
purple  is  a  much  stronger  modifier  of  vermihon  than  of  not-vermilion. 
Purple  may  be  described  as  a  "disproportionate  modifier"  of  vermil- 
ion, since  from  the  small  amount  of  its  effect  on  eye-color  when  acting 
alone  one  would  not  have  expected  the  great  effect  it  produces  when 
acting  in  the  presence  of  vermilion. 

This  type  of  intensification — disproportionate  modifier  and,  con- 
versely, differentiator — stands  midway  between  the  normal  relation 
where  combination  effects  are  roughly  proportional  to  the  separate 
effects,  so  that  both  genes  may  be  called  "general  modifiers,"  and  the 
special  relation  where  a  given  gene,  "specific  modifier,"  produces  by 
itself  no  visible  effect  whatever,  but  which  gives  a  more  or  less  marked 
effect  when  acting  in  conjunction  with  some  other  gene,  its  specific 
base,  sensitizer,  or  differentiator. 


OF   MUTANT    CHARACTERS. 


171 


In  order  to  make  full  use  of  this  differentiation  of  purple  versiLS  not- 
purple  by  vermilion,  it  is  necessary  that  all  flies  used  in  the  experiment 
should  be  made  homozygous  for  vermilion.  This  is  often  inconve- 
nient, and  accordingly  only  in  the  early  and  comparatively  simple 
experiments  was  this  method  employed.  It  was  soon  found  also  that 
the  separation  of  purple  from  red  was  not  causing  any  trouble,  so  that 
the  differentiation  in  this  case  has  little  net  advantage,  though  it  is 
still  of  interest  as  being  the  first  example  in  Drosophila  in  which  inten- 
sification was  recognized  and  deliberately  made  use  of. 

THE  RELATION  OF  PURPLE  TO  PINK. 

Some  of  the  first  purples  which  emerged  in  the  F2  were  crossed  to 
pink  to  test  whether  these  two  eye-colors  were  allelomorphic  or  not. 
Only  wild-type  Fi  males  and  females  were  produced  (table  26),  which 
showed  that  the  purple  is  not  an  allelomorph  of  pink. 

Table  26. — Fi  progeny  from  out-cross  of  purple. 


Apr.  17, 
1912. 

Wild- 
type  9- 

Wild- 
type  <f. 

B3.1.... 
B3.2.... 
B3.3.... 
B4 

Total 

33 

27 
23 
54 

31 
25 

28 
50 

137 

134 

THE  LINKAGE  OF  PURPLE  AND  VESTIGIAL. 

It  was  observed  (April  2,  1912;  Bl)  that  in  the  F2  from  the  cross  of 
the  original  male  to  wild  nearly  all  of  the  flies  that  were  purple  were 
also  vestigial.  This  observation,  following  on  the  heels  of  the  black- 
curved  case,  furnished  a  second  example  of  autosomal  linkage,  this 
time  one  of  so-called  "coupling,"  the  black  curved  case  having  been 
"repulsion."  No  full  counts  were  made  of  the  proportion  of  purples 
that  were  vestigial.  Indeed,  at  this  early  stage  the  linkage  relations 
were  receiving  less  attention  than  eye-color  "series." 

BACK-CROSS  TEST  OF  MALES.  PURPLE  VESTIGIAL  "COUPLING." 

The  advantages  of  the  back-cross  method  of  testing  linkage  and  the 
amount  of  crossing-over  had  only  begun  to  be  appreciated.  This 
method  had  been  applied  to  a  few  cases  in  the  X  chromosome,  and  the 
general  attack  upon  the  linkage  of  all  autosomal  mutations  planned 
by  Sturtevant  and  Bridges  (March  5,  1912)  contempkted  its  full  use. 
Thus  far  only  two  autosomal  back-crosses  had  been  completed — 
those  by  which  Sturtevant  showed  the  absence  of  linkage  between 
the  second  chromosome  and  the  third  chromosome  (balloon  ebony, 
May  10,  1912,  and  black  pink,  May  12,  1912).     Because  of  the  diffi- 


172 


THE    SECOND-CHROMOSOME    GROUP 


culty  of  getting  the  necessary  double  recessives  no  back-cross  which 
involved  autosomal  Unkage  had  been  possible  until  purple  arose  in 
the  vestigial  stock  and  thereby  gave  the  required  double  recessive, 
purple  vestigial,  with  which  such  a  test  of  the  amount  of  crossing- 
over  between  purple  and  vestigial  could  be  conducted.  From  the  F2 
described  above,  matings  were  made  which  gave  two  stocks  to  be 
used  in  this  test.  One  stock  was  the  simple  purple  vestigial  and  the 
other  was  purple  vestigial  pure  for  vermiHon.  The  special  advantage 
of  this  latter  stock  lay  in  the  fact  that  the  presence  of  vermiUon 
accentuates  the  difference  in  eye-color  between  the  flies  that  are 
purple  and  those  that  are  not;  that  is,  vermilion  purple  is  easier  to 
separate  from  vermilion  than  is  the  case  in  the  equivalent  separation 
of  purple  from  red. 

Table  27. — B.  C.  offspring  given  hy  the  Fi  (vermilion)  sons,  from  out-cross  of 
(vermilion)  purple  vestigial  males  to  vermilion  females,  when  back-crossed 
to  (vermilion)  purple  vestigial  females. 


June  24, 
1912. 

Non-cros3-overs. 

Cross-overs. 

(Vermilion) 

purple 

vestigial. 

(Vermilion.) 

(Vermilion) 
purple. 

(Vermilion) 
vestigial. 

BlO.l... 

'90 
71 

186 
202 

0 
0 

0 
0 

BIO. 2... 

'72 
l72 

197 
206 

0 
0 

0 
0 

Bll.l... 

r45 
L65 

126 
195 

0 
0 

0 
0 

^51 

88 

7 

3 

B11.2... 

98 

178 

27 

2 

43 

72 

4 

0 

B11.3... 

f54 

191 

0 

0 

Total 

L37 

70 

0 

0 

698 

1,711 

38 

5 

This  latter  stock  was  accordingly  used  in  the  Pi  mating  for  the  first 
back-cross  test.  VermiUon  purple  vestigial  males  were  out-crossed  to 
females  of  vermilion  stock  (May  25,  1912).  Both  parents  were  homo- 
zygous for  vermilion,  and  the  Fi  flies  were  all  vermilion,  as  expected. 
Both  purple  and  vestigial  are  recessive.  When  the  back-cross  matings 
came  to  be  made  the  culture  bottle  happened  to  contain  no  virgin  Fi 
females,  since  the  Pi  mating  had  been  niade  at  Columbia  and  the  Fi 
progenj'  used  had  hatched  en  route  to  Wood's  Hole.  The  back-cross 
was  therefore  made  in  only  one  way — by  mating  the  Fi  males  to  virgin 
vermilion  purple  vestigial  females  of  the  stock  kept  for  that  purpose. 
Five  back-crosses  were  started  by  mating  in  each  case  a  single  Fi  ver- 
milion male  by  two  or  three  stock  vermilion  purple  vestigial  females. 
At  the  end  of  10  days  the  parents  were  removed  from  the  culture 
bottles  and  put  in  fresh  bottles  in  which  second  broods  were  raised. 
In  one  case  a  third  brood  was  raised  (table  27). 


OF    MUTANT    CHARACTERS. 


173 


The  linkage  results  of  these  back-crosses  were  somewhat  unexpected, 
for  in  four  of  the  lines  no  cross-overs  at  all  were  obtained,  and  in 
another  only  a  few.  In  the  original  F2  culture  several  cross-oxers  had 
been  noted,  and  five  F2  cultures  raised  from  the  brothers  and  sisters  of 
these  back-crossed  males  seemed  to  be  giving  in  the  neighborhood  of 
15  per  cent  of  cross-overs  (table  28).  A  suspicion  was  aroused  that 
the  results  of  the  back-cross  and  of  the  F2  were  of  a  different  order, 
but  this  idea  did  not  develop  beyond  a  suspicion  because  of  the  con- 
tradictory result  given  by  the  different  back-cross  cultures.  It  was  not 
at  first  clearly  realized  that  these  aberrant  cultures  were  descended 
from  a  single  set  of  parents,  so  that  the  difference  was  disprojiortion- 
ately  blurred.  Whatever  difference  was  recognized  w-as  attributed  to  a 
possible  difference  in  the  linkage  results  given  by  back-crosses  as  con- 
trasted with  F2's.  Since  this  w'as  the  first  back-cross  invohing  auto- 
somal linkage  that  had  been  tried,  there  was  no  corrective  evidence  to 
show  that  these  two  kinds  of  results  might  not  be  different. 

Table  28. — F2  offspring  given  by  the  Fi  (vermilion)  sons  and  daughters  from 
the  out-cross  of  (vermilion)  purple  vestigial  males  to  vermilion  females. 


June  17, 
1912. 

(Vermilion). 

(Vermilion) 

purple 

vestigial. 

(Vermilion) 
purple. 

(Vermilion) 
vestiKial. 

B8.1.... 
B8.2.... 
B8.3.... 
B9.1.... 
B9.2.... 

Total 

200 
88 
255 
368 
346 

23 
21 
66 
19 
17 

9 
3 

25 
3 

19 

5 
4 
5 

7 
9 

1,257 

146 

59 

30 

BACK-CROSS  TEST  OF  FEMALES.  PURPLE  VESTIGIAL  "COUPLING." 

A  second  back-cross  experiment  using  the  simple  purple  vestigial 
stock  instead  of  the  vermilion  purple  vestigial  was  started  (June  25, 
1912)  a  month  later  than  the  first  and  before  the  results  of  the  first 
were  fully  known.  A  purple  vestigial  male  out-crossed  to  a  wild 
female  produced  wild-type  sons  and  daughters  (B  39;  -f-  9  15,  -}-  cf 
10).  Four  of  the  Fi  females  were  back-crossed  each  by  two  or  three 
purple- vestigial  males  from  stock.  In  this  case  Fi  females  happened 
to  be  chosen  because,  as  is  usually  the  case,  they  hatched  somewhat 
earlier  than  their  brothers  in  the  same  culture. 

These  back-cross  cultures  (table  29),  in  common  with  the  previous 
r2  cultures  (table  28),  showed  a  fair  amount  of  crossing-over  between 
purple  and  vestigial.  A  calculation  showed  that  the  percentage  of 
crossing-over  was  9.1.  This  was  recognized  as  being  of  a  different 
degree  from  the  apparent  percentage  of  1.8  calculated  from  the  first 
back-cross  (table  27).  It  was  now  reahzed  for  the  first  time  tliat  the 
two  back-crosses  had  differed  in  the  sex  of  the  Fi  flies  tested  by  the 


174 


THE   SECOND-CHROMOSOME    GROUP 


back-cross — that  the  first  back-cross  was  a  test  of  the  amount  of 
crossing-over  in  the  male  and  the  second  was  of  crossing-over  in 
females.  Up  to  this  time  there  had  been  no  suspicion  that  the  result 
of  a  back-cross  could  be  in  any  way  dependent  on  the  sex  of  the  Fi 
parent  used  in  the  experiment.  From  this  evidence  it  was  concluded 
that  there  was  crossing-over  in  the  male,  but  that  it  was  of  different 
degree  from  that  in  the  female.  In  September  1912,  Morgan  showed 
that  in  the  case  of  black  vestigial  no  crossing-over  whatever  had 

Table  29. — B.  C.  offspring  given  by  Fi  daughters,  from  the  out-cross  of  a 
purple  vestigial  male  to  a  wild  female,  when  hack-crossed  to  purple  vestigial 
males. 


July  16, 
1912. 

Non-cross-overs. 

Cross-overs. 

Purple 
vestigial. 

Wild- 
type. 

Purple. 

Vestigial. 

B36.1... 
B36.2... 
B39.1... 
B39.2.  .. 

Total 

82 
80 
32 
62 

163 

133 

53 

141 

12 

14 
3 
9 

15 
10 

7 
9 

256 

490 

38 

41 

occurred  in  the  male,  while  in  the  female  there  was  even  more  crossing- 
over  than  had  been  found  in  the  case  of  purple- vestigial.  Subsequent 
tests,  including  hundreds  of  thousands  of  individuals,  have  shown  that 
ordinarily  there  is  no  crossing-over  in  the  male  for  any  chromosome 
and  that  the  few  (2)  cases  that  have  occurred  were  probably  not 
brought  about  by  the  same  mechanism  as  that  by  which  crossing-over 
is  ordinarily  effected. 

NO  CROSSING-OVER  IN  THE  MALE. 

A  clear  conception  of  the  fact  of  no  crossing-over  in  the  male  was 
obscured  in  the  original  vermiUon  purple  vestigial  back-cross  test  by 
the  apparent  occurrence  of  cross-overs  in  one  of  the  five  cultures.  It 
is  still  a  matter  of  doubt  as  to  what  actually  occurred  in  that  culture. 
No  tests  were  made  of  the  apparent  cross-overs,  because  there  was  at 
that  time  no  evidence,  aside  from  the  inconsistency  within  the  experi- 
ment, to  suggest  that  they  were  very  unusual.  It  is  strongly  sug- 
gestive of  error  that  in  this  first  male  test,  carried  out  before  we 
were  on  guard,  so  many  apparent  cross-overs  should  have  occurred, 
and  that  in  the  numerous  and  extensive  tests  made  subsequently  they 
should  be  so  strikingly  absent.  Perhaps  some  clerical  error  was 
committed — such,  for  example,  as  a  mistake  in  labeling — that  this 
culture  was  really  one  of  the  F2  cultures  that  had  been  made  up  from 
the  same  Fi  culture,  though  at  a  different  time  from  the  back-crosses. 


OF    MUTANT    CHARACTERS.  175 

At  that  period,  it  is  true,  methods  of  keeping  records  were  poor  as 
compared  with  present  standards,  and  errors  were  all  too  frequent. 
Against  the  supposition  that  this  particular  mistake  was  made  is  the 
internal  evidence  that  the  proportion  of  vermilion  purple  vestigials 
in  the  questioned  culture  resembled  that  in  the  other  l^ack-cross 
cultures  and  is  larger  than  that  in  any  of  the  rightly  labeled  F2  cultures. 
Again,  that  this  culture  should  be  a  back-cross  test  of  the  female  rather 
than  of  the  male  would  require  a  double  error — i.e.,  as  to  the  sex  of 
both  parents— and  this  error  would  probably  have  been  detected  at  the 
time  of  the  transference  of  the  parents  to  fresh  culture-bottles,  espe- 
cially since  these  parents  w^ere  transferred  to  a  third  culture-bottle. 
The  suggestion  has  been  made  that  "maroon,"  a  third-chromosome 
recessive  eye-color  resembhng  purple  very  closely,  had  been  present, 
probably  only  in  heterozygous  form,  in  the  vermilion  purple  vestigial 
stock,  and  that  the  introduction  of  maroon  through  the  vermilion- 
purple  vestigial  parent  at  the  Pi  and  again  at  the  back-cross  mating 
would  account  for  the  cross-over  class  taken  to  be  vermilion  purple 
in  the  progeny.  Such  an  explanation  fails  to  account  for  the  comple- 
mentary class  of  exceptions,  the  few  but  carefully  attested  vestigials 
that  were  not-purple.  Several  other  suggestions  have  been  made, 
and  while  it  seems  highly  probable  in  the  light  of  the  more  recent 
work  that  these  apparent  cross-overs  were  really  due  to  error  in  the 
conduction  of  the  experiment  or  to  unknown  properties  of  the  stocks 
used,  none  of  the  suggested  escapes  from  the  alternative  that  there 
really  had  been  crossing-over  in  this  particular  Fi  male  have  solved 
all  the  difficulties. 

If  these  were  true  cross-overs,  it  is  still  possible  that  their  production 
should  have  no  relation  to  the  mechanism  by  which  crossing-over  is 
ordinarily  effected.  Thus,  Muller  (1916)  reported  a  case  of  crossing- 
over  in  the  back-cross  test  of  a  certain  Fi  male  from  the  mating  of 
truncate  to  black.  However,  all  of  the  gametes  of  this  particular  Fi 
male  proved  to  be  cross-overs,  so  that  crossing-over  must  have  occurred, 
once  for  all,  in  an  early  cell  of  the  embryo,  and,  as  usual,  no  crossing- 
over  whatever  occurred  during  spermatogenesis.  The  spermatozoa,  all 
of  which  were  descended  from  this  embryonic  cross-over  cell,  simply 
inherited  the  cross-over  combination.  In  the  case  of  purple  \'estigial 
a  like  explanation  would  apply,  except  that  in  this  case  the  crossing- 
over  occurred  in  a  somewhat  later  stage  of  the  embryo  and  in  conse- 
quence only  a  part  of  the  spermatogonial  cells  carried  the  cross-over 
combination,  and  only  sperm  descended  from  these  particular  cells 
produced  cross-over  progeny. 

That  somatic  crossing-over  has  httle  analogy  to  the  ordinary  type 
is  proved  by  a  similar  case  of  embryonic  crossing-over  in  the  female, 
which  was  followed  by  crossing-over  of  the  ordinary  type.     A  nrnting 


176  THE    SECOND-CHROMOSOME    GROUP 

was  made,  such  that  a  certain  class  of  daughters  should  all  have  the 

composition— — r r--     Seven  of  the  eight  daughters  tested 

had  this  expected  composition,  but  one  (No.  3464)  gave  only  offspring 

corresponding  to  the  composition  — - — j -r—.    That  is,  the  gene 

for  lethal  9  was  found  to  be  not  in  the  chromosome  in  which  it  entered 
the  zygote,  but  in  the  homologous  chromosome  derived  from  the  other 
parent.  As  in  the  truncate  X  black  case,  this  transmigration  took 
place  after  fertilization  and  so  early  in  the  embryonic  history  that  all 
the  germ-cells  were  descended  from  this  altered  cell.  A  significant 
feature  of  this  case  is  that  while  the  change  must  be  described  super- 
ficially as  double  crossing-over,  this  double  crossing-over  occurred 
within  a  region  only  10  units  long — a  space  shorter  than  that  in  which 
double  crossing-over  of  the  ordinary  type  has  ever  been  detected,  even 
in  certain  regions  of  the  autosomes  in  which  double  crossing-over  is 
relatively  frequent. 

OTHER  MUTATIONS. 

Tw'o  new  mutations  were  found  and  two  old  ones  recurred  in  these 
back-cross  experiments  on  the  linkage  of  purple  and  vestigial. 

"Kidney"  eye-shape,  a  third -chromosome  recessive,  was  found  in 
B.  C.  culture  B  102,  June  26,  1912  (table  27).  This  mutant,  the 
first  affecting  the  shape  or  texture  of  the  eye,  was  considerably  used 
in  the  early  days  (see  Morgan,  1914,  and  Bridges,  1915),  but  has  now 
been  superseded  by  mutants  less  variable  and  easier  to  classify. 

In  culture  B  39.2  it  was  noted,  July  26,  1912,  that  several  wild-type 
flies  had  more  bristles  on  the  thorax  than  the  regular  number,  ^.  e.,  4. 
Later  it  was  found  that  such  extra-bristled  flies  were  occurring  in 
small  proportions  in  all  four  sister  cultures,  from  which  it  would  appear 
that  the  mutation  was  a  recessive,  introduced  through  the  purple- 
vestigial  stock  used  twice  in  the  experiment.  The  extra  bristles 
occurred  among  all  classes  in  the  experiment  indifferently,  which 
would  seem  to  indicate  that  the  gene  was  not  second-chromosome, 
since  if  it  were  the  extras  should  have  been  relatively  more  frequent 
among  the  purple  vestigials.  The  number  of  extra  bristles  varied 
from  1  to  4,  the  highest  total  bristle  number  observed  being  8.  Extra 
bristles  were  also  observed  to  be  frequent  in  two  or  three  other  stocks. 
A  stock  throwing  extra  thoracic  bristles  derived  from  B  39.2  was  main- 
tained by  rough  mass  selection  for  some  time  and  was  finally  given  to 
Mr.  E.  C.  MacDowell  to  be  used  as  the  basis  of  rigorous  selection  experi- 
ments (MacDowell,  1915).  As  the  result  of  a  survey  of  all  stocks 
known  or  suspected  to  contain  extra  bristles,  MacDowell  chose  a  cer- 
tain wild  stock  as  the  most  favorable  starting-point  for  his  selection. 


OF   MUTANT   CHARACTERS.  177 

In  culture  B  9  a  jaunty  (jaunty  4)  appeared  which  gave  rise  to  a 
stock  similar  to  the  original  jaunty,  but  so  far  as  known  of  separate 
origin. 

In  three  or  four  of  the  cultures,  for  example  in  B  9.1,  arc  wings  (arc 
6)  appeared,  and  these  were  indistinguishable  from  the  original  arc, 
though  quite  certainly  of  different  origin. 

Since  these  early  experiments  many  other  mutations  have  arisen  in 
experiments  involving  purple,  but  these  need  no  special  mention  here. 

THE  INVIABILITY  OF  VESTIGIAL-PREMATURATION.  REPUGNANCE. 

LETHALS. 

One  of  the  most  striking  features  of  these  crosses  involving  purple 
and  vestigial  was  the  failure  of  vestigial  to  appear  in  as  high  a  propor- 
tion as  expected.  In  the  F2  (table  28)  where  25  per  cent  of  the  flies 
were  expected  to  be  vestigial,  only  12  per  cent  were  vestigLal;  in  the 
back-crosses,  where  half  of  the  flies  were  expected  to  be  vestigial,  only 
29  per  cent  (table  27)  and  36  per  cent  (table  29)  were  vestiguil;  that  is, 
only  about  half  as  many  vestigials  as  were  expected  appeared  in  these 
back-crosses. 

Such  a  condition  is  usually  described  by  the  blanket  term  "in via- 
bility;" but  a  consideration  of  the  " inviability "  met  with  in  the  case 
of  rudimentary  (Morgan,  1912)  had  just  led  to  two  new  conceptions: 
first,  that  the  power  of  fertilization  possessed  by  a  gamete  is  influenced 
by  its  somatic  environment  prior  to  maturation;  second,  that  a  given 
type  of  egg  is  less  likely  to  produce  a  viable  zygote  with  one  than  ^^'ith 
another  of  two  classes  of  sperm.  The  conception  of  "  prematuration  " 
was  used  to  account  for  the  fact  that  a  rudimentary-bearing  egg  from  a 
pure  inidimentary  female  is  much  less  able  to  give  a  viable  offspring 
than  a  like  egg  from  a  mother  only  heterozygous  for  rudimentary.  The 
principle  of  ''repugnance"  was  exemplified  by  the  cross  of  rudimentary 
by  rudimentary,  which  gave  no  offspring  whatever,  though  repeated 
fully  100  times,  and  although  both  the  male  and  female  give  offspring 
when  out-crossed.  The  rudimentary  females  are  usually  sterile,  and 
never  give  more  than  a  few  offspring  (nearly  all  females)  when  out- 
crossed  to  unrelated  males. 

The  shortage  of  vestigials  in  the  above  crosses  was  thought  to  be 
parallel  to  the  results  given  by  rudimentary,  except  that  in  the  case 
of  vestigial  the  effects  of  prematuration  and  repugnance  were  not  as 
great  in  degree.  On  the  basis  of  these  results,  an  analysis  of  the  extent 
to  which  each  of  these  principles  contribute  to  the  "inviability"  of 
vestigial  was  undertaken  by  Mr.  G.  L.  Carver  (results  not  yet  pub- 
lished). In  Mr.  Carver's  investigation  it  was  assumed  that  the  short- 
age in  these  experiments  had  been  largely  due  to  a  cause  intrinsic  in 
the  vestigial  itself,  for  which  reason  any  stock  of  vestigial  should  be 
equally  valid  for  the  test.  The  stocks  used  in  the  above  experiments 


178  THE   SECOND-CHROMOSOME    GROUP 

were  not  used,  because  they  were  full  of  odds  and  ends  of  mutants 
which  might  lead  to  confusion.  The  tests  showed  that  very  little 
prcmaturation  or  repugnance  is  inherent  in  vestigial,  the  ratios  being 
exceptionally  close  to  Mendelian  expectation;  wherefore  it  seems 
probable  that  the  shortage  met  with  in  the  purple  vestigial  experiments 
was  due  to  some  cause  peculiar  to  the  stocks  used  or  to  the  culture 
methods  used  in  the  experiments.  Later  tests  with  stocks  descended 
from  these  original  stocks  have  failed  to  give  such  aberrant  viability. 
Another  explanation  that  has  been  more  recently  appUed  to  partic- 
ular instances  in  which  a  character  ordinarily  of  excellent  viability  has 
not  appeared  in  the  expected  proportion,  is  that  of  a  lethal  gene.  Thus, 
an  autosomal  lethal  in  the  second  chromosome  quite  far  to  the 
right  of  vestigial  {i.  e.,  close  to  speck)  would  give  results  roughly- 
comparable  to  those  observed.  The  difficulty  with  such  an  explana- 
tion in  this  case  is  tliat  the  uniform  results  given  by  all  the  cultures 
would  require  the  lethal  to  be  present  in  nearly  all  the  indi\aduals, 
a  frequency  entirely  out  of  the  question  both  from  a  priori  consider- 
ations and  from  the  results  of  subsequent  tests  made  with  these  stocks. 

THE  PURPLE    "EPIDEMIC"— MUTATING  PERIODS. 

Shortly  after  the  discovery  of  purple,  purples  or  eye-colors  closely 
resembling  purple  began  to  be  found  in  stocks  and  experiments  every- 
where. In  the  interval  of  6  months  following  the  discovery  of  purple 
such  occurrences  numbered  14  and  furnished  the  first  as  well  as  the 
most  striking  of  the  "epidemics  of  mutation"  that  seemed  to  sweep 
over  our  material  at  this  period.  From  later  and  well-authenticated 
cases  (e.  g.,  vermilion,  cut,  notch,  etc.)  it  appears  that  certain  muta- 
tions do  recur,  and  in  the  case  of  cut,  four  independent  occurrences 
followed  one  another  so  closely  that  the  term  ''epidemic"  is  descrip- 
tive of  the  condition  observed.  How^ever,  in  the  early  cases  (purple, 
jaunty,  arc,  etc.)  it  is  certain  that  a  large  majority  of  the  apparent 
cases  were  not  true  recurrences  of  the  mutative  change,  but  were  due 
to  several  other  conditions.  Thus,  the  first,  fifth,  sixth,  and  thir- 
teenth of  the  apparent  purples  proved  to  be  maroon,  a  third-chromo- 
some ej'e-color  practically  indistinguishable  from  purple  in  appearance. 
That  is,  "mimic"  mutations  were  not  at  first  distinguished  from 
the  original  type,  nor  were  new  mutant  allelomorphs  distinguished  from 
types  already  known  unless  the  difference  was  striking.  Certain  others 
of  the  occurrences  were  proved  not  to  be  of  independent  origin ;  thus, 
purples  8  and  9  were  both  show^n  to  have  been  descended  from  a 
certain  common  stock,  and  purples  10  and  11  were  traced  to  a  second 
common  stock.  It  is  undoubtedly  true  that  in  many  cases  where  no 
connection  can  be  traced  such  connection  really  existed,  especially  in 
the  case  of  recessives,  which  might  be  distributed  without  giving  sign 
of  their  presence.  The  psychological  element,  too,  is  important;  it  is 
exceedingly  difficult  to  recognize  a  mutative  change,  even  a  striking 


OF   MUTANT    CHARACTERS. 


179 


one,  before  one  becomes  "sensitized"  to  that  particular  mutation. 
Some  of  our  mutant  characters  had  long  been  i)resent  in  stocks  or 
experiments,  so  that  many  flies  showing  the  cliaracter  must  liave  been 
seen,  before  attention  become  sharply  focused  upon  the  differences 
shown.  Contamination  and  errors  of  one  sort  or  another  liave  also 
added  to  the  number  of  apparent  reoccurrences  of  mutations.  It  is 
therefore  to  be  doubted  if  more  then  two  of  the  apparent  reoccur- 
rences of  purple  were  genuine  remutations. 

REPETITION  OF  THE  PURPLE  VESTIGIAL  BACK-CROSS  TESTS. 

Because  of  the  number  of  disturbing  conditions  that  had  been  met 
with  in  the  first  set  of  tests  of  the  linkage  of  purple  and  vestigial,  a 
second  and  more  extensive  set  was  started.  These  second  experi- 
ments were  carefully  planned,  and  in  the  results  obtained  approach 
present  standards  of  uniformity  and  reliability.  The  viability  of 
vestigial  w^as  excellent,  and  the  equality  of  contrarj^  classes  throughout 
the  experiments  speaks  for  the  favorable  culture  conditions.  The  new 
experiments  were  conducted  with  a  purple  vestigial  stock  descended 
from  that  used  in  the  experiments  of  table  28,  but  cleared  of  mutations 
and  perhaps  other  disturbing  factors  by  out-crossing  to  wild  and  by 
selection,  started  among  the  F2  progeny  and  maintained  for  several 
generations  until  it  seemed  probable  that  the  stock  was  clean.  Also, 
from  the  progeny  of  table  28  some  purple  (not-vestigial)  cross-overs 
were  selected  and  from  them  was  secured  in  a  few  generations  a  simple 
purple  stock  free  from  vestigial  and  from  the  other  mutant  characters 
known  to  be  present. 

Table  30. — F2  offspring  from  cross  of  a  purple  male  to  a  wild  female. 


Nov.  25, 
1912. 

Wild- 
type  9. 

Wild- 
type  cf  • 

Purple  9- 

Purple  cf . 

C  178.... 
0179.... 

118 
47 

81 
54 

35 
33 

32 
40 

300 

150 

A  preliminary  test  of  the  qualities  of  this  purple  stock  was  made  by 
out-crossing  a  male  to  a  wild  female  and  carefully  examining  all  Fj 
flies  (table  30).  The  F2  showed  only  purple  (150)  and  wild-ty]-)e 
flies  (300)  as  expected,  but  the  ratio  was  1  :  2  instead  of  1  :  3.  While 
this  deviation  was  significant  (4.1  times  the  probable  error),  it  indicated 
a  peculiarity  of  the  wild  parent  rather  than  of  the  purple,  and  was  not 
further  regarded.  The  vestigial  stock  used  was  that  from  which  pur- 
ple itself  was  derived.  It  had  been  examined  frequently  and  seemed 
to  be  clean. 

The  question  of  crossing-over  in  the  male  was  the  first  point  attacked. 
Complementary  Pi  matings  were  made  (June  13,  1913)  by  crossing 
purple  vestigial  to  wild  ("coupling")  and  by  crossing  purple  by  vesti- 


180 


THE    SECOND-CHROMOSOME    GROUP 


gial  ("repulsion").  Fi  males  from  these  matings  were  back-crossed 
singly  to  purple  vestigial  females  from  the  stock.  The  parents  were 
in  several  cases  transferred  at  the  end  of  10  days  to  fresh  culture- 
bottles  and  second  broods  then  raised. 

Table  31.' — B  C.  offspring  given  by  the  Fj  mid-type  sons,  from  the  out-cross 
of  a  purple  vestigial  male  to  a  wild  female,  when  hack-crossed  to  purple 
vestigial  females. 


July  7, 
1913. 

Non-cross-overs. 

Cross-overs. 

Purple 
vestigial. 

Wild- 
type. 

Purple. 

Vestigial. 

BQ 

DR 

DS 

DS' 

DT 

DT' 

DU 

Total 

62 
113 
131 
34 
89 
33 
90 

52 

141 

96 

28 

68 

22 

112 

0 
0 
0 
0 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 

552 

519 

0 

0 

'This  table  and  table  32  were  included  by  Morgan  in  his  paper  on  "No  crossing-over  in  the 
male  of  Drosophila   .    .    ."     Biol.  Bull.,  April,  1914,  pp.  200  and  201. 

The  offspring  from  the  ''coupling "  experiment  (5  pairs,  both  broods, 
table  31)  gave  a  total  of  1,071  flies,  not  one  of  which  was  a  cross-over, 
and  the  "repulsion"  experiment  (3  pairs,  both  broods,  table  32)  added 
704  more  (total,  1,775),  not  one  of  which  was  a  cross-over.  Since 
these  were  back-cross  experiments,  there  was  no  masking  of  results 
possible,  and  cross-over  gametes  had  every  opportunity  to  reveal 

Table  32. — B.  C.  offspring  given  by  Fi  wild-type  sons,  from  out-cross  of  purple 
male  to  vestigial  female,  when  back-crossed  to  purple  vestigial  females. 


July  7, 
1913. 

Non-cross-overs. 

Cross-overs. 

Purple. 

Vestigial. 

Purple 
vestigial. 

Wild- 
type. 

DV 

DV 

DW 

DX 

DX' 

Total 

62 
70 
61 

66 
79 

42 
78 
53 
103 
90 

0 
0 
0 
0 

0 

0 
0 
0 
0 
0 

346 

358 

0 

0 

themselves  had  any  been  formed,  so  that  each  fly  recorded  above  is  a 
true  non-cross-over.  While  the  total  absence  of  cross-overs  in  these 
repetitions  of  the  male  test  did  not  prove  that  the  apparent  cross-overs 
in  the  original  test  were  not  genuine,  it  added  to  the  already  large 
body  of  evidence  which  showed  that  they  were  at  least  aberrations 
from  the  normal  condition. 


II 


OF    MUTANT    CHARACTERS. 


181 


The  second  point  attacked  was  the  amount  of  crossing-over  in  the 
female  between  the  loci  purple  and  vestigial.  The  same  two  comple- 
mentary crosses  that  had  furnished  the  material  for  the  male  tests 
just  given  were  used  as  the  source  of  the  females  to  be  tested.  Fi 
daughters  from  these  two  matings  were  back-crossed  singly  to  purple- 
vestigial  males,  with  the  results  given  below. 

BALANCED  INVIABILITY-COMPLEMENTARY  CROSSES. 

The  reason  why  both  "coupHng"  and  ''repulsion"  experiments 
were  made  is  that  by  combining  the  two  sets  of  data  one  can  calculate 
a  linkage  value  more  nearly  free  from  the  errors  due  to  dispropor- 
tionate inviability  of  any  class  (Bridges,  1915,  Muller,1916).  Within 
each  back-cross  the  inviability  effects  due  to  a  given  mutant  form  are 
largely  neutralized.  Since  the  inviable  form  occurs  both  as  a  cross- 
over and  as  a  non-cross-over,  both  of  these  classes  are  lowered,  but 
lowered  proportionately,  so  that  the  linkage  ratio  remains  practically 

Table  33. — B.  C.  offspring  given  by  Fi  mild-type  daughters,  from  out-cross  of 
purple  vestigial  male  to  wild  female,  when  back-crossed  to  purple  vestigial  males. 


Julys, 
1913. 

Non-cross-overs. 

Cross-overs. 

Per  cent  of 
cross-overs. 

Change 
with  age. 

Purple 
vestigial. 

Wild-type. 

Purple. 

Vestigial. 

DA 

DA' 

DB 

DB' 

DC 

DC 

DD 

DD' 

DE 

DE' 

DF 

DF' 

DG 

DC 

DH 

DH' 

Firsts 

Seconds .  . 

178 
152 
91 
69 
165 
191 
140 
116 
191 
196 
202 
197 
105 
188 
123 
129 

202 
227 
100 
104 
150 
216 
149 
122 
214 
229 
226 
228 
158 
232 
140 
179 

16 
13 
18 
12 
17 
18 
20 
9 
20 
11 
20 
25 
17 
17 
26 
11 

16 
14 
13 

8 
19 
17 
15 

4 
19 
22 
22 
20 
17 
14 
30 
20 

7.8 

6.6 

14.0 

10.3 

10.3 

7.9 

10.8 

5.2 

9.0 

7.2 

8.9 

9.6 

11.4 

6.9 

17.6 

9.1 

-1.2 

-3.7 

-2.4 

-5.6 

-1.8 

-HO. 7 

-4.5 

-S.5 

1,195 
1,238 

1,339 
1,539 

154 
116 

151 
119 

10.7 

7.8 

-2.9 

undisturbed.  This  internal  balancing  holds  less  well  for  combinations 
of  characters;  for  any  given  combination  occurs  in  an  experiment 
either  as  a  cross-over  or  as  a  non-cross-over,  but  not  as  both,  and 
should  any  combination  have  an  inviability  disproportionate  to  tliat 
of  the  component  mutant  forms,  then  the  cross-over  value  would  be 
disturbed.  The  remedy  for  this  condition  is  to  balance  the  experi- 
ments in  which  a  relatively  inviable  class  occurs  as  a  cross-over  by  an 
equal  amount  of  data  in  which  this  same  class  is  a  non-cross-over.     It 


182 


THE    SECOND-CHROMOSOME    GROUP 


is  often  not  convenient  or  possible  to  have  complementary  crosses  of 
equal  weight;  but  whatever  is  done  in  that  direction,  however  little, 
is  of  advantage,  and  even  a  partially  balanced  result  is  to  be  preferred 
to  one  from  only  one  type  of  cross.  With  improvements  in  culture 
methods,  inviability  effects  have  been  very  much  reduced  everywhere. 
Also,  with  the  great  increase  in  the  number  of  mutations,  there  is  now 
provided  an  abundance  of  forms  which  show  only  negligible  inviability. 
Our  regular  work  utilizes  only  these  viable  forms,  and  except  for  very 
special  purposes  those  mutants  which  show  more  than  a  slight  invia- 
bility are  avoided. 

Table  34. — B.  C.  offspring  given  hj  Fi  wild-type  daughters,  from  the  out- cross  of 
a  purple  male  to  a  vestigial  female,  when  hack-crossed  to  purple  vestigial  males. 


July  5, 
1913. 

Non-cross-overs. 

Cross- 

overs. 

Per  cent  of 
cross-overs. 

Change 
with  age. 

Purple. 

Vestigial. 

Purple 

vestigial 

Wild-type. 

DI 

DI' 

DJ 

DJ' 

DK 

DK' 

DM 

DM' 

DN 

DN' 

DO 

DO' 

Firsts 

Seconds. . 

157 
200 
198 
242 
252 
198 
205 
213 
66 
66 
189 
217 

178 
165 
176 
195 
227 
178 
158 
246 
54 
64 
172 
225 

26 
12 
23 
19 
34 
26 
27 
14 
6 
4 
30 
13 

21 
14 
23 
26 
38 
20 
32 
23 
11 
7 
32 
18 

12.3 

6.7 
11.0 

9.3 
13.1 
10.9 
14.0 

7.4 
12.4 

7.8 
14.6 

6.5 

-5.6 

-1.7 

-2.2 

-6.6 

-4.6 

-8.1 

1,067 
1,136 

965 
1,073 

146 

88 

157 
108 

13.0 

8.1 

-4.9 

The  first  back-crosses  of  purple-vestigial  had  shown  a  marked 
inviability  for  vestigial  and  a  slight  amount  for  purple.  The  new 
back-crosses  showed  practically  no  inviability  for  purple  and  a  very 
moderate  amount  for  vestigial,  but  still  enough  to  repay  the  added 
labor  required  by  the  balancing  cross.  As  in  the  first  back-cross  test 
of  the  female,  the  linkage  shown  was  fairly  strong.  Since  the  linkage 
shown  by  second  broods  proved  to  be  different  from  that  of  firsts,  only 
first  broods  will  be  considered  for  the  moment.  The  ''coupling" 
experiment  (table  33)  gave  a  total  of  2,839  first-brood  flies,  of  which 
305  or  10.7  per  cent  were  cross-overs.  The  ''repulsion"  first  broods 
(table  34)  gave  a  total  of  2,335  flies,  of  which  303  or  13.0  per  cent  were 
cross-overs.  When  the  first  brood  data  from  both  these  experiments 
are  combined,  so  that  the  inviability  is  balanced,  the  cross-over  value 
is  1 1.8  (608  cross-overs  in  a  total  of  5,174.) 

These  two  component  cross-over  values  differed  slightly  from  each 
other  and  from  the  value  (9.1)  obtained  in  the  original  experiment. 
It  may  be  questioned  whether  the  difference  in  the  cross-over  values 


OF   MUTANT   CHARACTERS.  183 

was  entirely  due  to  inviability.  Slight  differences  of  this  order,  but 
many  of  them  undoubtedly  significant,  are  continually  appearing  in 
our  work.  Other  known  causes  of  linkage  variation  besides  inviability 
are:  differences  in  the  age  of  parents  (Bridges,  1915)  or  of  the  tempera- 
tures at  which  the  experiments  are  conducted  (Plough,  1917),  or 
mutant  "cross-over"  genes  (Sturtevant,  Muller,  and  Bridges),  and 
probably  to  several  other  internal  and  external  factors  not  yet  analyzed. 
The  best  that  can  be  done  in  correction  is  to  calculate  mean  values 
from  as  many  experiments  as  possible  where  none  of  the  recognized 
causes  of  variation  are  especially  active,  and  thus  obtain  a  sort  of 
composite  picture  of  the  "normal"  condition. 

THE  VARIATION  IN  CROSSING-OVER  WITH  AGE. 

The  reason  for  raising  second  broods  in  these  experiments  was  to 
obtain  more  offspring  from  each  female  and  thus  secure  a  more  trust- 
worthy index  of  the  genetic  behavior  of  individual.  This  practice  was 
extended  to  all  the  work  at  this  time,  and  was  continued  until  a  compar- 
ison of  the  cross-over  values  of  the  first  and  second  broods  brought  out 
a  remarkable  relation  in  the  cases  involving  the  second  chromosome. 
There  was  found  to  be  a  change  in  the  amount  of  crossing-over,  so 
that  both  in  the  totals  for  each  experiment  and  in  a  great  majority  of 
the  individual  cultures  the  cross-over  value  had  fallen  significantly. 
Equally  surprising  was  the  fact  that  there  was  no  such  change  in  the 
case  of  the  first  chromosome,  and  this  added  another  proof  of  the 
distinctness  of  our  linkage  groups — that  is,  of  the  individuality  of  the 
chromosome  involved.  The  first  case  in  which  this  decrease  for  the 
second  chromosome  was  clearly  seen  was  that  of  the  back-cross  tests 
of  the  purple  vestigial  linkage  given  in  tables  33  and  34.  Of  the  8 
females  whose  tests  are  given  in  table  33,  seven  showed  a  decrease  in 
percentage  of  crossing-over  and  only  one  (F)  showed  an  increase, 
which,  however,  was  smaller  in  amount  than  the  smallest  of  the 
decreases.  In  the  complementary  case  "repulsion"  (table  34)  all  6 
females  showed  a  decided  drop.  The  totals  likewise  reflected  this 
same  change;  the  decreases  were  2.9  and  4.9  units  respectively.  The 
cross-over  value  calculated  from  the  balanced  second  broods  was  8.0, 
a  decrease  of  3.8  units,  or,  compared  with  the  corresponding  cross- 
over value  (11.8)  from  the  balanced  first  broods,  a  32  per  cent  decrease 
from  the  normal  amount.  Many  other  experiments  have  confirmed 
the  fact  of  change  in  crossing-over  frequency  with  the  age  of  the 
mother,  and  a  partial  analysis  has  been  made. 

THE  LOCUS  OF  PURPLE-A  TWO-POINT  MAP. 

The  repetition  of  the  purple  vestigial  back-crosses  was  not  carried 
out  until  the  summer  of  1913;  meanwhile  considerable  progress  had 
been  made  with,  the  mapping  of  the  second  chromosome.     The  test 


■  I 


184 


THE    SECOND-CHROMOSOME    GROUP 


of  the  amount  of  crossing-over  in  the  female  between  the  loci  purple 
and  vestigial  (table  29)  had  given  a  cross-over  value  of  9.1  units.  The 
next  cross-over  value  to  be  worked  out  was  that  of  black  vestigial  as 
about  20  imits  (Morgan,  1912).  With  these  two  values  alone  it  was 
not  possible  to  determine  the  relative  order  within  the  chromosome  of 
the  three  loci  involved;  it  was  apparent  that  black  was  farther  away 
from  vestigial  than  from  purple,  but  it  could  not  be  told  whether  it  lay 

Table  35. — Pi  mating,  'purple  cf  X  black  9  ;  Fi  mating, 
wild-type  9  9  and  cf  cf . 


Oct.  24, 

1912. 

F2, 

Wild- 
type. 

Black. 

Purple. 

Black 
purple. 

C68 

0  69 

C70 

Total 

248 
278 
158 

137 

103 

60 

136 

157 

78 

0 
0 
0 

684 

300 

371 

0 

on  the  same  or  on  the  other  side  of  vestigial  from  purple.  The  black 
purple  value  should  be  one  of  two  values  depending  on  the  order  of  the 
genes;  it  should  be  an  approximation  to  either  the  sum  (20 -|- 9  =  29)  or 
the  difference  (20  —  9  =  11)  between  the  black  vestigial  and  the  purple 
vestigial  values.  To  carry  out  a  back-cross  experiment  for  black  and 
purple  it  was  first  necessary  to  make  up  the  double  recessive.  No 
easy  task  was  anticipated  in  this,  for  it  had  just  become  known  that 
on  account  of  no  crossing-over  in  the  male  no  double  recessive  could  be 

Table  36. — Pi  mating,  purple  cf  X  black  9;  B.C.,  Pi  9    X  black  purple  cf . 


B.  C.  of  9 , 

Dec.  12, 

1912. 

Non-cross-overs. 

Cross-overs. 

Black. 

Purple. 

Black 
purple. 

Wild- 
type. 

C174.... 
Ill 

Total .  . 

320 
33 

339 
43 

13 
3 

18 
4 

353 

382 

16 

22 

obtained  in  F2,  as  in  fact  none  was  (table  35).  As  expected,  the  F2 
ratio  approximated  2:1:1:0.  Three  sorts  of  F3  mass-culture 
matings  were  made:  black  X  bla,ck,  purple  X  purple,  and  black  X 
purple.  Of  these  matings  the  last  type  is  by  far  the  most  valuable, 
since  in  case  one  of  the  flies  happened  to  come  from  a  black  purple 
cross-over  egg  X  a  black  sperm  it  would  give  some  purple  offspring 
when  crossed  to  purple;  and  these,  inbred,  would  give  the  required 
black  purples  as  a  quarter  of  the  next  generation.  Likewise,  if  one 
of  the  purples  had  come  from  a  cross-over  black  purple  egg,  the  black 
X  purple  cross  would  produce  some  blacks  that  would  give  the  required 


OF   MUTANT   CHARACTERS. 


185 


black  purples  upon  inbreeding.  If  both  the  black  and  the  purple 
chosen  happened  to  have  come  from  cross-over  eggs,  then  the  double 
would  be  produced  in  F3  directly.  In  case  none  of  the  parents  proved 
to  be  from  cross-over  gametes,  than  at  least  the  F3  wild-type  flies  are 
equivalent  to  the  Fi  and  would  save  a  generation  in  the  repetition. 
The  other  two  types  of  crosses  would  give  a  favorable  result  only  if 
both  parents  happened  to  be  from  cross-over  eggs,  in  which  ca.se  the 
double  would  appear  among  their  progeny. 

Table  37.— Pi  mating,  purple,  cf  X  black  9 ;  B.C.,FicP  X  black  purple  9  . 


B.C.of  cf, 

Dec.  12, 

1914. 

Non-cross-overs. 

Cross-overs 
(cf  test). 

Black. 

Purple. 

Black 
purple. 

Wild- 
type. 

112 

74 

71 

0 

0 

It  so  happened  that  one  of  the  black  X  black  crosses  gave  a  few 
black  purples  in  F3  directly  and  from  these  a  stock  was  made  for 
use  in  back-crossing.  At  the  same  time  a  Pi  mating  of  a  black  male 
to  a  purple  female  was  started  to  furnish  the  required  Fi  hetero- 
zygotes.  A  single  test  of  the  Fi  male  showed,  as  expected,  no  crossing- 
over  whatever  (table  37), 

Two  back-cross  tests  of  the  female  gave  a  total  of  773  flies,  of  which 
38  or  4.9  per  cent  were  cross-overs  (table  36).  Of  the  two  expected 
values,  that  of  30  is  excluded  entirely,  and  that  of  10  is  approximated, 
though  not  very  closely.  On  this  basis,  the  order  of  these  genes  is 
black,  purple,  vestigial,  and  not  black,  vestigial,  purple. 

A  THREE-POINT  BACK-CROSS.  BLACK  PURPLE  CURVED.  WITH 

BALANCED  INVIABILITY. 

Most  of  the  linkage  experiments  up  to  this  time  had  involved  only 
two  loci,  as  the  three  just  cited,  namely,  purple  vestigial,  black  ves- 
tigial, and  black  purple.  It  was  now  realized  that  a  more  complex 
type  of  experiment  involving  all  three  loci  at  once  would  yield  returns 
whose  value  far  outweighed  the  greater  labor  entailed.  Thus,  a 
multiple  back-cross  for  black  purple  vestigial  would  give  hnkage  data 
upon  all  three  cross-over  values  simultaneously,  and  these  values 
would  be  strictly  comparable,  since  there  would  be  no  possibihty  of 
discrepancies  due  to  different  conditions  of  culture  or  parentage. 
Accordingly,  the  simple  black  purple  back-cross  was  done  on  a  scale 
only  large  enough  to  decide  between  two  possible  values  and  thus  show 
what  was  the  order  of  the  three  loci.  A  knowledge  of  this  order  is  of 
great  advantage  in  synthesizing  the  multiple  recessive.  It  was  found, 
as  already  stated,  that  black  and  vestigial  are  the  two  farthest  apart  and 


186 


THE   SECOND-CHROMOSOME    GROUP 


the  mating  was  accordingly  arranged  so  that  a  cross-over  anywhere 
within  this  whole  distance  would  give  the  required  triple  form.  That 
is,  black  purple  and  purple  vestigial  were  mated  together  and  the 

resulting   purple   offspring  (^7^ — J  were  inbred.     The  F2  black 

Table  38. — Pi  mating,  black  purple  vestigial  d^   X  wild  female;  B.  C.  mating 
Fi  wild-type  9   X  black  purple  vestigial  cf . 


Jan.  9, 
1914. 

b         Pr 

Vg 

b      1 

6     Pr 

1 

b        \                       \        Vg 

1      Pr      Vg 

1 

Pr      1 

Black 

purple 

vestigial. 

Wild- 
type. 

Black. 

Purple 
vestigial. 

Black 

purple 

vestigial. 

Vestigial. 

Black 
vestigial. 

Purple. 

II  141 

II  142 

II  143 

Total .... 

89 

118 

61 

140 

137 

78 

3 
3 
2 

1 
3 
4 

11 
15 
12 

12 

9 

11 

1 

1 

268 

355 

8 

8 

38 

32 

1 

1 

Table  39. — Pi,  black  X  purple  vestigial;  B.  C.  test  of  Fi  9  9  singly. 


Mar.  9, 
1914. 

b 

Pr                     Vg 

b       \        Pr              Vg 

b                           1         Vg 

Pr         1 

1              1           "ff 

88 

103 

104 

115 

116 

Total .... 

114 
92 
99 
97 

164 

96 

81 
98 
66 

77 

10 

15 

11 

2 

6 

10 
5 
15 
12 
15 

7 
12 

8 
14 
12 

15 
16 
17 
13 
19 

1 

1 
0 
0 
2 

1 
0 
0 

1 

0 

566 

418 

44 

57 

53 

80 

4 

2 

Table  40. — ^Pi,  black  vestigial  X  purple;  B.  C.  test  Pi  9  9  singly. 


Mar.  10, 
1914. 

b 

^g 

b\Pr 

b               1 

b     1     P, 

1           Vg 

Pr 

1 

Pr        1        "» 

1             1 

101 

102 

112 

113 

Total .  .  . 

85 

137 

67 

92 

126 

133 

68 

1.37 

10 
13 

7 
13 

7 
13 

7 
8 

23 
16 
12 
21 

15 
23 

8 
9 

1 
0 
0 
1 

0 
0 

1 

1 

381 

464 

43 

35 

72 

55 

2 

2 

purples  and  purple  vestigials  were  crossed  together  in  several  mass- 
cultures,  and  in  Fa  some  triples  occurred,  showing  that  some  of  both 
kinds  of  F2  flies  used  had  come  from  cross-over  eggs.  A  better  method 
would  have  been  to  back-cross  the  Fi  female  by  a  black-vestigial  male. 
In  this  case  every  black  vestigial  cross-over  would  be  known  to  be  of 

— ^'    ^^   ),  and  these  inbred  would  give  the  pure 

h  -^  Vg     / 


the  composition 


( 


OF    MUTANT    CHARACTERS. 


187 


triple  without  the  chance  of  failure  entailed  by  method  actually  used. 
A  stock  of  black  purple  vestigial  was  made  from  the  triple  reeessives 
that  hatched  in  Fg  (March  1913). 

In  carrying  out  the  triple  back-cross,  the  principle  of  balancing  the 
inviability  by  complementary  crosses  was  applied.  To  comi)letely 
balance  a  three-locus  experiment  requires  four  types  of  crosses,  so  that 
every  class  may  appear  in  each  of  the  four  cross-over  categories, 
namely,  (0)  non-cross-overs,  (1)  cross-overs  in  the  first  region,  that 

Table  41. — Pi,  black  purple  X  vestigial;  B.  C.  o/  Fi  9  9  singly.    . 


Oct.  28, 

h          Pr 

b  1 

'V 

b           p, 

1      'V 

b\ 

1 

1914. 

Vg 

1    Pr 

1 

\Pr 

|r. 

654 

130 

152 

10 

5 

14 

10 

0 

0 

670 

124 

HI 

10 

8 

11 

14 

1 

1 

671 

137 

138 

15 

6 

12 

30 

2 

2 

672 

131 

154 

7 

10 

18 

12 

0 

1 

673 

162 

151 

11 

7 

12 

13 

2 

0 

674 

Total .... 

159 

162 

8 

7 

16 

24 

0 

2 

843 

868 

61 

43 

83 

103 

5 

6 

Table  42. — Summary  of  the  four  types  of  black  purple  vestigial  back-cross, 

with  inviability  balanced. 


Combinations. 

0 

1 

2 

1.  2 

Total. 

b         Pr 

'V 

268           355 

8               8 

38 

32 

1 

1 

711 

b 

623 

16 

70 

2 

566           418 

44           57 

33 

80 

4 

2 

1,224 

Pr 
b          Pr 

IV 

984 

101 

133 

6 

843           868 

61           43 

83 

103 

5 

6 

2,012 

b 

Vg 

1,711 

104 

186 

11 

381           464 

43           35 

72 

55 

2 

2 

1,054 

Pr 
Total 

845 

78 

127 

4 

4,163 

299 

516 

23 

5,001 

between  black  and  purple,  (2)  cross-overs  in  the  second  region,  that 
between  purple  and  vestigial,  and  (1,  2)  double  cross-overs,  the  simul- 
taneous occurrences  of  crossing-over  in  both  regions.  Thus,  the  cross 
of  black  purple  vestigial  by  wild  and  the  back-cross  of  the  Fi  wild-type 
daughters  by  the  triple-recessive  male  gave  one  of  the  four  types  of 
crosses  (table  38).  The  other  types  of  experiment  carried  out  were 
black  by  purple  vestigial  (table  39),  black  vestigial  by  purple  (table 
40),  and  black  purple  by  vestigial  (table  41).  In  order  that  these 
four  crosses  should  balance  closely,  the  same  number  of  cultures  (6) 


188  THE    SECOND-CHROMOSOME    GROUP 

was  started  in  each  case.  A  few  of  these  cultures  failed,  and  the  total 
data  in  the  separate  experiments  are  consequently  not  in  equal  amounts. 
The  balance  is  for  this  reason  not  perfect,  though  such  partially  bal- 
anced results  are  far  better  than  an  equal  amount  of  data  secured  from 
only  one  of  the  four  possible  types  of  experiment.  Additional  cultures 
could  have  been  raised  until  a  balance  was  reached,  and  such  a  practice 
has  been  followed  in  other  cases,  for  example,  the  vermiUon  sable 
forked  case  reported  by  Morgan  and  Bridges  (1916).  A  summary 
of  these  complementary  crosses  appears  in  table  42,  from  which  the 
following  balanced  cross-over  values  are  calculated:  black  purple 
6.4,  purple  vestigial  10.8,  and  black  vestigial  16.3. 

COINCIDENCE. 

Another  and  very  important  advantage  of  these  more  complex 
crosses  is  that  the  process  of  double  crossing-over  can  be  examined. 
Thus  there  were  23  double  cross-overs,  or  0.46  per  cent  of  the  total 
flies.  If  the  proportion  of  double  cross-overs  were  determined  by 
chance  alone  the  percentage  should  have  been  6.4  per  cent  of  10.8  per 
cent  or  0.69  per  cent  of  the  total.  The  observed  per  cent  of  coincident 
cross-overs  (0.46)  is  only  61  per  cent  of  the  theoretical  per  cent  (0.69). 
This  percentage,  61,  is  called  the  "coincidence"  for  black  purple 
vestigial.  This  index  can  be  more  conveniently  calculated  directly 
from  the  back-cross  numbers  as  follows  (see  Weinstein,  1918) : 

No.  of  doubles  X  Total  flies  X  100     23  X  5001  X  100 


Total  firsts  X  Total  seconds  322  x  539 


■  =  61.3 


THE  RELATION  BETWEEN  COINCIDENCE  AND  MAP-DISTANCE. 

The  coincidence  of  61  observed  in  this  case  is  relatively  very  high. 
A  coincidence  under  5  is  expected  for  cases  in  the  first  chromosome 
where  similar  map-distances  are  involved.  This  higher  coincidence 
may  mean  that  for  some  reason  the  freedom  of  crossing-over  is  much 
less  in  this  region  of  the  second  chromosome  than  it  is  in  the  first 
chromosome.  The  17.5  units  of  map-distance  between  black  and 
vestigial  may  correspond  to  as  great  a  length  of  actual  chromosome 
as  is  involved  in  cases  in  the  first  chromosome  where  the  coincidence 
is  the  same,  but  the  map-distances  are  nearly  three  times  as  great.  On 
the  other  hand,  instead  of  the  higher  coincidence  being  due  to  a  lower 
"coefficient  of  crossing-over,"  it  may  be  due  to  a  relatively  short 
"average  internode."  The  length  of  chromosome  represented  by  a 
given  map-distance  may  be  the  same  in  the  two  regions  compared, 
but  in  the  second  chromosome  the  mechanism  of  double  crossing-over 
may  not  require  so  long  a  section  of  chromosome  between  successive 
cross-overs.  If  the  average  length  of  the  internode  was  shorter 
because  of  this  closer  spacing  of  doubles,  then  a  greater  proportion  of 
doubles  would  occur  in  the  given  region  from  black  to  vestigial,  and 
coincidence  would  be  correspondingly  higher.     However,  the  interest 


OF    MUTANT    CHARACTERS.  189 

of  these  problems  in  double  crossing-over  is  out  of  all  proportion  to  our 
progress  in  their  solutions. 

It  seems  likely  that  a  more  satisfactory  method  of  expressing 
these  relations  may  be  derived  than  is  provided  by  the  present  form- 
ula; the  new  formulation  must  take  account  of  separate  factors  analyz- 
able  in  the  process  and  permit  their  adequate  representation.  The 
conclusions  based  on  the  old  formula  must  be  regarded  as  provisional. 

THE  USE  OF  PURPLE  IN  MAPPING  OTHER  GENES-CURVED. 

STREAK.  ETC. 

The  "map"  of  the  second  chromosome  began  to  be  useful  when  the 
order  and  spacing  for  the  three  genes,  black,  purple,  and  vestigial, 
were  roughly  established  by  the  determination  of  the  third  value,  that 
for  black  purple  (December  1912).  The  three-locus  experiment  just 
given  provided  more  accurate  measures  of  the  map-distances  involved. 
The  preparation  of  the  multiple  recessive  and  of  the  Pi  stocks  delayed 
the  completion  of  this  experiment  for  nearly  a  year  (January  1914). 
Meanwhile,  these  provisional  locations  were  used  as  the  basis  for 
locating  other  genes  more  closely.  The  first  of  these  was  curved. 
Bridges  and  Sturtevant  (Biol.  Bull.,  1914)  soon  found  (January  1913) 
that  black  and  curved  gave  approximately  23  per  cent  of  crossing- 
over.  The  next  point  to  be  determined  was  the  relation  of  curved 
and  one  of  the  other  two  mutations  whose  loci  had  been  mapped. 
Both  of  these  tests  were  used,  since  each  offered  advantages;  the  chief 
disadvantage  was  that  vestigial  interferes  with  the  classification  of 
curved,  so  that  it  is  impossible  to  distinguish  between  the  simple 
vestigials  and  the  vestigial  curved  class. 

The  purple  curved  test  was  undertaken  by  Bridges,  who  prepared  to 
run  a  three-point  back-cross  involving  black,  purple,  and  curved.  The 
first  step  was  the  synthesis  of  the  purple  curved  double  recessive.  As 
soon  as  this  was  obtained  it  was  turned  over  to  Mr.  W.  S.  Adkins,  who 
ran  a  preliminary  back-cross  test  of  the  simple  purple  curved  crossing- 
over,  and  found  that  there  was  about  18  per  cent  of  crossing-over. 
This  enabled  us  to  determine  the  relation  of  curved  to  the  other  three 
genes.  The  purple  curved  value  of  18  showed  that  curved  was  closer 
to  purple  than  to  black  (black  curved  =  23)  and  that  purple  and  vesti- 
gial were  therefore  "to  the  right"  of  black.  Curved  was  further  to 
the  right  than  vestigial,  since  black  and  vestigial  gave  only  about  18 
per  cent  of  crossing-over. 

The  vestigial  curved  distance  was  tested  by  Sturtevant,  who  found 
that  there  was  about  8.5  per  cent  of  crossing-over.  Because  of  the 
difficulty  of  classification  already  referred  to,  it  was  not  thought  worth 
while  to  run  these  tests  on  a  large  scale.  However,  vestigial  is  itself 
accurately  mapped  and  is  nearer  to  curved  than  purple  is,  and  these 
considerations  are  strong  enough  so  that  the  vestigial  curved  tests  will 


190 


THE    SECOND-CHROMOSOME    GROUP 


ultimntely  be  extended  and  may  furnish  the  main  basis  for  the  accurate 
mapping  of  curved. 

Meanwhile,  the  purple  curved  test,  while  less  satisfactory  because 
of  the  longer  interval  with  the  attendant  correction  necessary  for 
double  crossing-over,  was  more  readily  handled,  and  this  led  to  a  rapid 
accumulation  of  data  on  the  purple  curved  cross-over  value.  The 
black  purple  curved  triple  recessive  was  obfained  (May  1913),  and  the 
back-cross  itself  carried  out.  Thirteen  of  the  Fi  wild-type  daughters 
from  the  cross  of  black  purple  curved  to  wild  were  tested  by  back- 
crossing  singly  to  males  of  the  triple  form.  These  same  parents  were 
at  the  end  of  10  days  transferred  to  fresh  culture-bottles  and  second 
broods  were  raised.  The  details  of  the  data  of  these  cultures  have 
already  been  published  (Bridges,  1915),  and  we  need  repeat  here  only 
the  totals  for  the  first  broods  (table  43). 

Table  43. — Total  offspring  in  the  first  broods  of  the  black  purple  curved  X 
wild  back-cross  (details  published  J.  E.  Z.,  July  1913,  p.  8). 


b        Pr        c 

1 

6 

b   Vt 

1 

H 

\c 

Total. 

b    Pr 
value. 

Pr    C 
value. 

b  c 
value. 

1  Pt<^ 

1    c 

Pr    1 

Autr.  24, 
1913... 

1,476 

1,577 

96 

74 

339 

330 

19 

23 

3,934 

5.4 

18.1 

21.3 

The  second  broods  confirmed  on  a  large  scale  the  fact  first  brought 
to  light  in  the  purple  vestigial  back-cross  (table  33),  that  in  the  second 
chromosome  the  amount  of  crossing-over  changes  with  the  age  of  the 
mother  (see  Bridges,  1915). 

The  numerical  relations  in  the  first  broods  of  this  experiment  con- 
firmed the  position  of  curved  as  already  mapped.  A  map  of  the  second 
chromosome  was  constructed  on  the  basis  of  the  data  then  on  hand 
(October  1913),  and  was  as  follows: 

h  Pr  Vg  c 


0.0         5.3  17.5  25.0 

The  black  purple  curved  back-cross  was  carried  out  in  only  one  of 
the  four  possible  ways,  and  is  therefore  unbalanced.  However,  the 
results  showed  that  inviability  was  negligible.  Wliat  little  deviation 
there  was  from  expectation  can  be  attributed  to  curved,  which  still 
appeared  to  the  extent  of  97  flies  for  every  100  expected. 

ALTERNATED  BACK-CROSSES. 

In  cases  where  only  one  type  of  back-cross  is  to  be  made,  the  poorest 
type  is  that  in  which  all  the  mutants  are  together,  as  was  the  case  in 
the  black  purple  curved  X  Tvdld  experiment  just  cited.  The  flies 
having  the  most  mutant  characters  are  relatively  the  least  viable,  and 
this  type  of  cross  furnishes  the  highest  proportion  of  such  individuals. 


I 


OF   MUTANT   CHARACTERS. 


191 


The  best  type  is  that  known  as  "alternated, "  where  the  successive  genes 


alternate  between  the  two  chromosomes 


b    +    c 


,  so  that  the  nuix- 


+      Vr      + 

imum  of  evenness  of  distribution  of  characters  is  attained.  It  re(}uires 
double  crossing-over  to  put  all  the  mutant  characters  in  the  same 
individual,  and  accordingly  the  alternated  experiment  gives  a  minimum 
number  of  the  combinations  that  are  most  inviable.  This  i)rinciple 
becomes  still  more  important  in  more  complex  experiments,  as,  for 

example, ■ ■ -• 

+      d     +    p,   +     Px    + 

The  next  mutant  whose  locus  was  mapped  with  reference  to  purple 
as  a  base  was  "streak,"  a  dominant  character  which  shows  as  a  dark 
streak  from  the  scutellum  forward  along  the  dorsal  region  of  the  thorax. 

Table  44. — Streak  purple  curved  hack-cross  data. 


Combinations. 

Total. 

0 

1 

2 

1.  2 

Coincidence. 

Si 

Pt      c 
St        Vr 

c 

Total 

878 
929 

435 
496 

247 
254 

127 
117 

69 
62 

98.0 
102.0 

1,807 

931 

501 

244 

131 

100.2 

The  triple  black-cross  streak  purple  curved,  which  was  made  in  two 
of  the  four  possible  ways  and  is  therefore  partially  balanced  (table  44), 
showed  that  streak  is  far  to  the  left  of  purple,  that  is,  beyond  black,  and 
in  the  opposite  direction  from  vestigial  and  curved.  The  streak 
purple  cross-over  value  was  35.0,  which  showed  that  streak  is  so  far  to 
the  left  of  purple  that  only  an  approximate  calculation  of  its  position 
could  be  made  from  the  data.  In  a  region  of  such  length  the  correc- 
tion to  be  supplied  because  of  double  crossing-over  is  quite  large  and 
correspondingly  inexact.  On  the  basis  of  data  tliat  ha^'e  since  become 
available  it  appears  that  there  is  about  37.3  per  cent  of  separation 
between  streak  and  purple.  Purple  has  since  played  an  important 
role  in  the  mapping  of  several  other  genes,  the  details  of  which  will 
appear  in  accounts  of  these  mutations. 

A  SUMMARY  OF  THE  LINKAGE  DATA  INVOLVING  PURPLE. 

Besides  the  data  reported  in  the  various  sections  of  this  paper,  there 
are  available  data  from  three  other  principal  papers:  Bridges's  study 
of  age  variation  in  crossing-over  (J.  E.  Z.,  1915),  Aluller's  study  of  cross- 
ing-over by  means  of  the  progeny  test  (Am.  Nat.,  191G),  and  Plough's 
study  of  temperature  variations  in  crossing-over  (J.  E.  Z.,   1917). 


192 


THE    SECOND-CHROMOSOME    GROUP 


Table  45  gives  a  detailed  summary  of  all  these  data  collected  according 
to  two  loci  calculations.  The  black  purple  cross-over  value  of  6.2 
based  on  48,931  flies  places  the  locus  of  purple  at  6.2  units  to  the  right 
of  black,  or  at  52.7  when  referred  to  star  as  the  zero-point. 

Table  45. — Summary  of  purple  cross-over  data. 


Loci. 


Star  purple. . . 


Streak  purple. 


Dachs  purple . 


Black  purple. 


Purple  vestigial 


Purple  curved 


Purple  plexus . 
Purple  arc 


Total. 


6,766 


1,027 


362 


8,155 


1,807 
462 
396 


2,665 


462 


1,027 


1,489 


773 

3,934 

5,001 

462 

.36,622 

2,1.30 


4>^,931 


825 
2,839 

2,335 

5,001 

462 

2,1.39 


13,601 


3,934 
1,807 

462 

952 

36,622 

6,766 
593 


Cross- 
overs. 


51,136 


344 
2,625 


3,010 


413 


138 


3,561 


632 
137 
114 


883 


97 


196 


293 


38 
212 
322 

26 

2,214 

214 


3,026 


79 
305 

303 

539 

60 

323 


Per 
cent. 


1,609 


711 
375 

90 

182 

7,222 

1,508 
117 


10,205 


164 
1,066 


44.5 


40.2 


38.1 


43.7 


35.0 
29.7 

28.8 


33.1 


21.0 


19.1 


19.7 


4.9 
5.4 


6.4 

5.6 

6.0 

10.0 


6.2 


9.1 
10.7 

13.0 

10.8 
13.0 
15.1 


11.8 


18.1 
20.7 

19.5 
19.1 
19.7 

22.3 
19.7 


Date. 


19.9 


47.7 
40.6 


July  11,  1915 

Aug.  24,  1916 
July  21,  1917 

Nov.  6,  1913 
May  — .  1914 
Aug.  24,  1916 

May—,  1914 
Aug.  14,  1916 


Dec.  12,  1912 
Aug.  28,  1913 
Jan.  9,  1914 
May  — ,  1914 
Jan.  5,  1915 
Mar.    5,  1917 


July  16,  1912 
July    5,  1913 

July     5,  1913 

Jan.  9,  1914 
May—,  1914 
Mar.  5,  1917 

Aug.  24,  1913 
Nov.  6.  1913 

May  — ,  1914 
Aug.  24,  1914 
Jan.     5, 1915 

Feb.  11,  1915 
Feb.    8, 1916 

Feb.  29,  1916 
Oct.  24,  1914 


By 


Bridges . 


Do. 
Do. 

Bridges . 
Muller. . 
Bridges . 


Muller. 


Bridges . 


Bridges. 

Do. 

Do. 
Muller . . 
Plough . 

Do. 


Bridges . 
Do. 

Do. 

Do. 

Muller . 
Plough . 


Bridges . 
Do. 

Muller . , 
Bridges . 
Plough . 


Bridges . 
Do. 

Bridges . 
Do. 


Reference. 


S'; 


S' 


-B.C.,  Ists;  1836-1894. 


Pr  c  Sp 

S'  Pr 

S';  — ^ — J-  B.C.;  4999-5110. 

S' 

S':  B.C.;  7391-2. 

Pr 

Sk;      Sk      pr    c    balanced     B.C.; 

II  103-124. 
Am.  Nat.,  1916,  p.  422. 


S'; 


S' 


Pr 


St 
4999-5110. 


B.C.,    Sk   only 


Am.  Nat.,  1916,  p.  422. 


S'; 


S' 


Pr 


Sk 


-j-    B.C.;  4999-5110. 


Pr;  b  Pr  B.C.;  C  174-11  2. 

Pr;  b  Pr  c  B.C.,  Ists;  II  58-11  88. 

Pr;  b  p,.i!j  balanced  B.C.;  II 141-674 

Am.  Nat.  1916,  p.  422. 

J.E.Z.  1917,  total  bprc  B.C.  contro 

J.E.Z.  1917,  toialb PrVgB.C.  contro 

Pr;  Pr  vg  B.C.;  B  36.1-B  39.2. 
Pr;  Pr  Vg  B.C. ;  DA-DH. 

Pr;  ^   B.C.;  DI-DO. 

Vg 

Pr;  b  Pr  Vg  balanced  B.C. ;  II 141-67' 
Am.  Nat.,  1916,  p.  422. 
J.E.Z.,    1917,    total    b    Pr    vg  B.C 
controls. 

Pr;  6  Pr  c  B.C.  Ists;  II  58-11  88. 
St;     St    Pr    c    balanced     B.C.; 

II  103-11  124. 
Am.  Nat.,  1916,  p.  422. 
sp;  Pr  c  Sp  B.C.;  452-508. 
J.E.Z.,  1917,  b  PrC  B.C.  controls. 

S' 

S';  B.C.  Ists;  1836-'9 

Pr    C    Sp 

llla;  PrCSpF2;32i)3-'8. 


llla;  Pr  Px  Sp  F2;  3535-'53. 
Pt 


^'       a  Si 


B.C.  637-686. 


OF    MUTANT    CHARACTERS. 


193 


Table  45. — Summary  of  purple  cross-over  data — continued. 


Loci. 

Total. 

Cross- 
overs. 

Per 
cent. 

jrple  speck.  . 

462 
9>'32 

218 
410 

47.2 
43.1 

2,625 

1,166 

44.4 

6,766 

3, 1.30 

46.3 

259 

95 

36.7 

565 

279 

49.4 

356 

176 

49.4 

1 1 , 985 

5 .  474 

45.7 

tirple  balloon . 

462 

218 

47.2 

Date. 

By- 

May  — ,  1914 
Aug.  24,  1914 

Mullcr 

Bridges 

Oct:  24,  1914 

Do. 

July  11,  l'.)15 

Do. 

Feb.     7, 1916 

Do. 

Feb.     8,  1916 
Feb.  29, 1916 

Do. 
Do. 

May—.  1914 

Muller 

Reference. 


Am.  Nat.,  1910,  p.  422. 
«p;  Pr  c  8p  B.C. ;  452-608. 

— B.C.:  637-680. 


a; 


S':- 


Pt      C      8p 

Pr  »B 


B.C.  lBtfl;p.  18.36-'»4. 


i//a.--777;--F,:3168-. 

Ijja;  h  c  sp  Fj;  3203-'8. 
llln:  Pt  Px  "p  Fi;  :i53.S-'53. 


Am.  Nat.,  1916,  p.  422. 


SPECIAL  PROBLEMS  INVOLVING  PURPLE-AGE-VARIATIONS.  COINCI- 
DENCE. TEMPERATURE-VARIATIONS.  CROSS-OVER  MUTATIONS, 
PROGENY  TEST  FOR  CROSSING-OVER. 

We  have  already  seen  how  the  study  of  the  age- variation  in  crossing- 
over  for  the  second  chromosome  began  with  the  purple  vestigial  back- 
cross  (p.  181)  and  was  continued  and  confirmed  by  the  black  purple 
curved  triple  back-cross  (p.  185).  Some  of  the  early  data  suggested 
that  the  drop  in  the  second  broods  was  followed  by  a  recovery  and 
perhaps  even  by  a  rise  in  later  broods  (Bridges,  1915). 

To  gain  further  light  on  the  course  of  the  variation  throughout  the 
Hfe  of  the  fly  a  special  and  extensive  experiment  was  continued  through 
four  broods.     The  entire  length  of  the  chromosome  was  covered  by  the 

{- )• 

This  experiment  showed  the  normal  cross-over  values  for  the  first 
broods,  the  usual  drop  for  the  second  broods,  and  a  slight  continued 
drop  for  the  third  and  fourth  broods.  However,  the  experiment 
proved  inconclusive  because  of  two  ill-adaptations:  the  chromosome 
distances  involved  were  so  long  (e.  g.,  S'  pr  =  52.7)  that  real  changes 
could  be  concealed  by  a  concomitant  change  in  double  crossing-over, 
and  further  because  the  10-day  broods  gave  only  four  points  on  the 
curve  of  age-variation,  each  point  representing  only  the  net  change 
for  a  10-day  period,  while  the  real  underlying  curve  may  have  changed 
its  course  so  that  an  unknown  part  of  each  10-day  period  may  have 
been  a  fall  and  the  rest  a  rise. 

The  original  black  purple  curved  experiment  had  avoided  one  of 
these  difficulties  in  that  the  black-purple  distance  is  so  short  tliat  there 


loci  chosen 


194 


THE   SECOND-CHROMOSOME   GROUP 


is  probably  no  double  crossing-over  whatever  within  it.  The  second 
difficulty  was  met  by  Plough  in  his  similar  studies  on  the  temperature 
variation  of  linkage,  by  transferring  his  parents  every  2  days  instead  of 
every  10  (Plough,  1917).  As  one  of  his  control  experiments  Plough 
ran  a  black  purple  curved  back-cross  of  13  pairs,  transferring  each 
pair  to  a  fresh  culture-tube  every  2  days  as  long  as  the  female  lived 
(table  14,  Plough,  1917).  The  plotted  curve  of  the  percentages  of 
crossing-over  between  black  and  purple  shows  an  initial  high  value 
(8  per  cent)  which  during  the  first  9  days  falls  rapidly  at  first  and  then 
more  slowly  to  a  low  value  (5  per  cent),  which  is  maintained  with  little 
change  to  about  the  sixteenth  day.  A  sharp  rise  then  sets  in  which 
reaches  its  maximum  (8  per  cent)  at  about  the  twenty-first  day.  The 
succeeding  fall  is  again  slow,  reaching  its  minimum  (3.5  per  cent)  at 
about  the  thirtieth  day.  Beyond  this  point  the  curve  again  rises 
slightly;  but  the  data  were  too  few  to  be  significant  beyond  about  the 
twenty-fifth  day.  While  there  was  some  variation  in  the  amount  and 
rapidity  of  these  changes  in  the  various  individual  curves,  all  showed 
the  same  typical  rhythm,  which  must  be  the  expression  of  fundamental 
physiological  changes  in  the  development  of  the  female.  It  seema 
possible  and  probable  that  these  successive  falls  and  rises  are  not  effects 
of  a  single  continuously  varying  physiological  process,  but  are  rather 
to  be  explained  as  separate  phenomena  caused  by  the  lapse  of  certain 
conditions  and  the  subsequent  onset  of  new  causes.  These  changes 
may  therefore  be  really  discontinuous  and  the  rhythmic  curve  only  a 
succession  of  independent  but  overlapping  variations. 

The  most  interesting  feature  of  the  age-variation  is  the  bearing  it 
has  on  the  problem  of  double  crossing-over  and  the  underlying  problems 
of  the  nature  of  crossing-over.  The  more  that  consideration  has  been 
given  to  this  problem  of  double  crossing-over  in  relation  to  chromosome 
and  to  map-distances,  the  more  involved  it  has  appeared,  so  that  no 
evidence  upon  these  points  can  be  neglected.  The  special  value  of 
such  cases  as  that  of  age-variation  is  that  they  enable  one  to  compare 
two  different  conditions  but  with  the  elimination  of  one  important 
variable;  for  the  actual  chromosome-distance  between  such  genes  as 
black  and  purple  is  maintained  constant,  so  that  any  variations  that 
occur  in  map-distance,  coincidence,  etc.,  must  be  due  to  variations  in 
one  or  more  of  the  other  factors.  This  relation  was  discussed  in  con- 
nection with  the  original  two-brood  black  purple  curved  cross  (Bridges, 
1915),  and  it  was  pointed  out  that  the  rise  in  coincidence  concomitant 
with  the  fall  in  crossing  over  meant  that  the  internode  length  had 
changed — that  the  two  cross-overs  of  a  double  no  longer  included 
the  same  average  length  of  chromosome,  but  a  longer  length.     The 

S' 

coincidences  of  the  case  support  this  view,  but  in  neither 

Pr  c  s^ 


OF   MUTANT   CHARACTERS.  195 

case  are  the  data  conclusive.  A  calculation  of  tlie  coincidence  shown 
by  Plough's  black  purple  curved  2-day  tube-cultures  has  provided 
data  considerably  more  satisfactory,  though  still  subject  to  a  high 
probable  error.  On  the  basis  of  all  the  data  it  is  probable,  not  only 
that  coincidence  varies  with  age,  but  that  the  curve  of  age-variation 
in  coincidence  is  roughly  the  mirror  image  of  the  curve  of  age  variations 
in  crossing-over.  While  it  seems  probable  that  at  least  part  of  the 
explanation  of  the  age-variations  both  in  crossing-over  and  in  coinci- 
dence has  been  found  in  an  internode  variation  as  suggested,  yet  in 
any  case  there  is  provided  evidence  of  a  common  cause  that  should 
repay  further  analysis. 

A  second  problem  involving  purple  and  very  closely  allied  to  the 
age-variation  in  conception,  material,  methods,  and  bearing  is  that 
of  the  temperature- variation  described  by  Plough  (1917).  Since  the 
genie  constitution  of  a  female  showing  the  age-variation  is  constant 
throughout  the  course  of  this  variation,  the  immediate  causes  of  the 
variations  must  be  regarded  as  environmental  dififerences  arising 
through  rhythmic  changes  in  the  physiological  processes  of  nutrition 
and  development.  While  the  crossing-over  variations  due  to  age  and 
to  specific  genes  were  effected  through  en\'ironmental  changes  arising 
internally,  they  suggested  the  possibility  that  similar  variations  might 
be  initiated  by  environmental  changes  arising  externally.  Plough 
found  that  exposure  to  abnormally  high  or  low  temperature  actually 
did  produce  linkage  change  even  more  extreme  than  those  due  to  age 
changes.  Black-purple-curved  back-cross  cultures  were  paired  at 
various  temperatures  from  9°  to  32°  C.  When  the  black-purple  cross- 
over values  were  plotted  it  was  seen  that  at  a  low  temperature  (9°), 
crossing-over  is  very  free  (14  per  cent)  and  becomes  even  more  free  at 
13°  (18  per  cent).  The  amount  of  crossing-over  then  falls  away  very 
rapidly,  and  at  18°  is  nearly  the  normal  value  (6.0  per  cent).  This 
value  is  maintained  to  about  27°,  or  throughout  the  range  of  "room" 
temperature  at  which  the  breeding  work  is  ordinarily  conducted.     At 

I  29°  the  crossing-over  is  slightly  freer  than  normal,  but  between  29° 

j  and  31°  the  amount  of  crossing-over  nearly  trebles  (18.2  per  cent). 

I  This  extraordinarily  sharp  and  extensive  rise  is  followed  by  a  slight 
fall  at  32°  (15.4  per  cent).  Above  this  temperature  and  below  9°  C. 
it  was  found  that  the  flies  either  died  or  produced  too  few  ofTspring  to 

'be  workable.  It  seems  probable  that  here  also  these  two  sharply 
marked  maxima,  separated  by  a  long  interval  of  no  or  slight  change, 
may  represent  two  distinct  phenomena. 

When  the  coincidences  are  calculated  for  these  various  temperatures 
it  is  seen  that  the  curve  of  temperature- variation  of  coincidence  is  a 
slightly  rising  but  practically  straight  line  cutting  alike  through  both 
of  the  maxima  and  the  normal  interval.     This  is  a  significant  difTerence 


y 


196  THE    SECOND-CHROMOSOME    GROUP 

from  the  relation  previously  observed  in  the  age- variations,  and  would 
seem  to  indicate  that  the  age  and  temperature  variations  were  accom- 
plished by  different  mechanisms — by  effects  upon  different  physio- 
logical factors.  Those  double  cross-overs  that  do  occur  have  the  same 
distribution  along  the  chromosome  at  all  temperatures,  which  shows 
that  the  method  of  handling  the  chromosomes  is  unchanged.  In 
accordance  with  the  analysis  already  given  (p.  188),  the  cause  of  the 
temperature  variations  in  crossing-over  is  to  be  sought  rather  in  vari- 
ation in  the  coefficient  of  crossing-over — in  the  crossing-over  capacity 
of  the  chromosome  itself,  because  of  some  variations  in  its  structure  or 
framework.  Just  as  in  the  relation  between  the  coincidence  and 
temperature  curves  discussed  before,  the  coincidence  curve  calcu- 
lated for  such  a  tube-count  temperature-time  curve  apparently  cuts 
through  the  rise  and  fall  due  to  temperature  instead  of  being  altered 
concomitantly  with  it. 

The  conclusion  just  drawn  from  the  failure  of  the  temperature- 
variation  to  affect  the  coincidence,  namely,  that  the  change  in  the 
amount  of  crossing-over  is  probably  due  to  a  change  in  the  physical 
properties  of  the  chromosome  subi^ance,  has  an  important  bearing 
on  the  question  of  the  stage  at  which  crossing-over  itself  occurs,  as 
follows :  From  a  study  of  the  time  taken  for  the  effects  of  exposure  to 
abnormal  temperature  to  become  manifest  or  to  disappear.  Plough 
concluded  that  the  effect  was  produced  at  one  stage  only  in  the  devel- 
opment of  the  ovary,  and  that  eggs  which  have  not  arrived  at  or  have 
passed  this  critical  stage  are  incapable  of  registering  any  temperature- 
variation.  It  was  next  argued  that  this  critical  stage  is  that  at  which 
crossing-over  itself  normally  occurs.  It  seems  certain  that  crossing- 
over  does  not  take  place  before  this  critical  stage  is  reached,  but  it 
does  not  follow  that  it  might  not  occur  at  some  stage  between  this  and 
the  maturation  divisions,  that  is,  at  any  later  stage  during  the  growth 
period.  At  the  critical  stage  one  of  the  factors  which  modifies  the 
frequency  of  the  crossing-over  becomes  fixed,  but  the  crossing-over 
itself  may  occur  later.  As  a  crude  analogy,  the  process  of  crossing-over 
might  be  likened  to  a  machine,  say  a  saw-mill.  The  rate  at  which 
boards  are  sawn  depends,  other  factors  remaining  constant,  upon 
the  toughness  of  the  log  fed  against  the  saws,  which  toughness  is  a 
physical  property  of  the  log  fixed  long  previously. 

The  coincidence  analysis  indicates  that  the  setting  of  the  crossing- 
over  machine  has  not  been  altered,  but  that  the  chromosome  at  a  i 
specific  sensitive  stage  in  its  fabrication  has  been  modified  in  one  of  | 
its  properties — its  toughness,  let  us  say — so  that  when  it  ultimately 
undergoes  crossing-over  the  output  is  different. 

It  is  quite  pos^ble  that  the  crossing-over  follows  immediately  after 
the  determination  of  this  property;  indeed,  from  other  lines  of  evidence 


OF    MUTANT    CHARACTERS.  197 

it  seems  probable  that  crossing-over  occurs  at  a  thin-thread  stage,  or 
at  least  that  the  characteristic  transjunction  is  accomplished  at  a 
leptotene  stage,  such  as  occurs  only  in  the  early  growth-period,  liut 
such  a  conception  does  not  exclude  the  possibility  that  the  crossing- 
over  occurs  at  a  four-strand  stage,  as  is  indicated  by  still  other  lines 
of  evidence.  To  call  such  an  early-growth-stage,  thin-thread,  four- 
strand  hypothesis  of  crossing-over  "  chiasmatj^De "  would  be  mislead- 
ing, since  the  term  is  usually  understood  as  applying  to  a  late-growth- 
stage,  thick-thread,  four-strand  condition.  The  term  "tetralepto- 
tenic"  might  be  used  for  this  type  of  crossing-over  to  distinguish  it 
from  both  the  dileptolenic  and  the  chiasmatype  hypotheses. 

Plough's  e\'idence  that  the  critical  stage  and  crossing-over  occur 
after  most  or  probably  all  of  the  oogonial  divisions  have  been  completed 
effectually  disproves  the  reduplication  hypothesis  of  crossing-over  as 
far  as  any  application  to  Drosophila  is  concerned,  for  the  number  of 
divisions  required  by  that  hypothesis  is  not  available. 

Purple  has  been  extensively  used  in  two  other  important  studies  on 
crossing-over — that  of  Sturtevant  upon  inherited  crossing-over  vari- 
ations (Part  III  of  this  volume),  and  that  of  IMuller  in  his  progeny 
test  of  a  multiple  heterozygote  in  studying  crossing-over.   (]Muller,  1916). 

SUMMARY  AND  VALUATION  OF  PURPLE. 

Of  the  200  or  more  mutations  in  Drosophila,  certain  ones  have  proved 
especially  useful  as  working  tools  because  of  excellent  characteristics 
or  favorable  location  in  the  chromosome.  Certain  others  have  an 
even  higher  interest  because  of  their  intimate  connection  with  the 
development  of  principles  or  subjects  that  have  now  come  to  be  the 
groundwork  of  every  Drosophila  experiment. 

As  a  working  tool  the  second-chromosome  recessive  eye-color  purple 
has  deserved  its  very  extensive  usage.  In  viability,  fertility,  produc- 
tivity, and  in  the  details  of  habit — ease  of  handling,  activity,  time  of 
hatching,  length  of  life,  etc. — purple  measures  well  up  to  the  standard 
of  the  wild  fly.  In  separability  from  the  wild-type,  purple  is  satisfac- 
tory both  in  certainty  and  in  speed.  The  only  faiUng  in  certainty 
is  that  arising  from  the  occurrence  in  the  same  culture  of  a  similar  eye- 
color — a  "mimic"  or  "pseudo-purple" — either  by  mutation  or  by 
introduction.  However,  the  presence  of  a  "mimic"  is  generally  easily 
recognized  and  such  difficulties  in  classification  are  only  temporary. 
The  ease  and  rapidity  of  separation  fail  to  be  satisfactory  with  purples 
older  than  about  3  days,  though  rarely  is  there  any  need  for  separa- 
tions so  delayed.  The  usefulness  of  purple  has  not  been  restricted  by 
"masking"  effects.  Until  very  recently  there  has  been  no  other 
readily  workable  second-chromosome  eye-color  so  similar  to  purple  in 
appearance  as  to  prevent  the  use  of  both  in  the  same  experiment 


198  THE   SECOND-CHROMOSOME    GROUP 

Without  confusion  between  them.  Purple  is  not  so  dilute  that  it  would 
interfere  with  the  classification  of  other  eye-colors,  as  does  ''white" 
in  the  X  chromosome;  nor  conversely  is  there  any  other  second-chro- 
mosome eye-color  so  dilute,  or  morphological  change  so  extreme,  as  to 
interfere  with  the  classification  of  purple  in  flies  possessing  both 
characters.  The  recessiveness  of  purple  seems  to  be  complete  and 
constant,  so  that  the  chance  of  confusion  between  it  and  the  heterozy- 
gote  is  nil. 

The  locus  of  purple  on  the  basis  of  very  extensive  data  is  6.2  units 
to  the  right  of  black,  or,  referred  to  star  as  a  base,  at  52.7.  Purple  is 
not  far  from  the  middle  of  the  second  chromosome  as  mapped,  and  is 
thus  within  striking  distance  of  mutant  loci  near  either  end  or  anywhere 
throughout  the  chromosome.  Its  closeness  to  black  (which  is  the 
primary  base  in  the  mapping  of  the  second  chromosome,  and  another 
of  the  very  best  characters)  furnishes  a  working  distance  which  is 
short  enough  to  exclude  double  crossing-over  and  long  enough  to  avoid 
the  excessive  probable  errors  incident  to  very  small  percentages  of 
cross-overs.  Outside  this  black-purple  section  the  second  chromosome 
is  as  yet  mostly  mapped  in  distances  too  great  or  too  small  to  handle 
satisfactorily  in  special  tests.  Furthermore,  it  appears  that  this  purple 
region  is  peculiarly  sensitive,  as  is  proved  by  its  exceptionally  high 
double  crossing-over  (this  paper),  by  its  greater  disturbance  by  age 
(Bridges,  1915;  Plough,  1917),  by  temperature  (Plough,  1917),  and  by 
its  unique  reaction  to  genetic  variations  in  crossing-over  (Sturtevant, 
Part  III  of  this  volume) .  The  explanation  of  this  sensitiveness  is  prob- 
ably that  this  region  is  actually  near  the  middle  of  the  chromosome 
with  the  spindle  fiber  attachment,  and  that  this  middle  region  is  the 
last  part  to  undergo  synapsis. 

The  number  of  subjects  in  the  genetics  of  Drosophila  toward  whose 
early  and  continued  development  purple  has  contributed  is  surprisingly 
large. 

In  the  field  of  mutation  it  gave  with  vermilion  the  first  case  in  which 
"intensification"  or  ''disproportionate  modification"  was  recognized 
and  made  use  of.  It  was  the  first  of  the  class  of  "dark"  eye-color 
mutations.  It  has  been  one  of  the  most  popular  models  in  Drosophila 
for  "mimic"  mutations.  The  most  striking  "epidemic  of  mutation" 
or  "mutating  period"  was  that  inaugurated  by  purple. 

In  the  early  experiments  involving  purple  several  other  mutations 
arose,  probably  the  most  interesting  of  which  was  "extra  bristles," 
which  led  to  the  study  made  by  MacDowell  on  the  effect  of  selection 
on  bristle  number,  ^ 

In  the  attack  upon  the  problem  of  "inviability"  purple  entered  into 
the  first  experiment  planned  to  include  the  balancing  of  inviability  by 
complementary  crosses.     This  practice  was  extended  to  involve  three 


OF   MUTANT   CHARACTERS.  199 

locus  experiments  in  the  balancing  of  the  black  purple  vestiKLil  back- 
cross.  The  inviabiUty  of  vestigial  met  with  in  the  early  purple  vesti- 
gial crosses  seems  not  to  have  been  due  primarily  to  " prematura! ion," 
"repugnance,"  or  autosomal  lethals,  but  probably  to  culture  condi- 
tions, as  shown  by  Carver  (unpublished). 

In  the  development  of  autosomal  linkage,  purple  was  involved  in  the 
first  coupling  F2  back-cross  test  of  crossing-over  in  the  male,  and  like- 
wise in  the  female.  One  of  these  back-cross  tests  of  the  male  gave  a 
few  apparent  cross-overs  which  prevented  a  clear  conception  of  "non- 
crossing  over  in  the  male."  The  back-cross  tests  of  the  female  gave 
the  first  "two-point"  autosomal  map,  purple  vestigml.  The  first 
autosomal  "three-point"  map  was  black  purple  vestigial,  completed 
by  the  determination  of  the  black-purple  cross-over  value. 

With  that  most  fascinating  and  difficult  subject — the  analysis  of 
the  relation  between  the  physical  chromosome  and  the  process  of 
crossing-over — purple  has  been  intimately  connected.  The  relatively 
high  coincidences  obtained  in  the  cases  of  black  purple  curved  and 
black  purple  vestigial  soon  showed  that  this  relationship  in  the  purple 
region  of  the  second  chromosome  is  different  from  the  relationship  for 
sections  of  like  map-distance  in  compared  regions  of  the  first  chromo- 
some. An  explanation  of  this  comparative  study  should  aid  in  arriving 
at  the  cause  of  the  differences. 

A  study  in  the  case  of  black  purple  curved  of  the  change  in  coinci- 
dence accompanying  the  age  variation  in  crossing-over  (Bridges,  1915) 
led  to  the  tentative  conclusion  that  both  changes  were  mainly  due  to 
a  lengthening  of  the  average  length  of  the  section  of  chromosome 
between  simultaneous  cross-overs,  rather  than  to  a  change  in  the 

S' 
freedom  of  crossing-over.     Certain  other  experiments,  notably , 

Pr  c  Sp 

which  give  information  on  the  age  and  coincidence  changes,  have 
given  results  that  agree  better  with  the  first  interpretation,  though  they 
do  not  exclude  the  alternative.  The  clearest  evidence  in  favor  of  the 
internode  change  is  derived  from  the  experiment  made  by  Plough  as 
a  control  for  his  temperature-change  cultures  (&  p,.  c  B.  C,  22°,  2-day 
interval  tube-control).  In  this  experiment  the  curve  for  varmtion 
in  coincidence  was  the  mirror  image  of  the  curve  of  variation  in  age. 
The  curve  of  coincidence  corresponding  to  the  curve  of  temperature 
variation  found  by  Plough  seems  to  be  a  straight  line  cutting  through 
the  rises  and  falls  of  the  temperature  curve  and  independent  of  them. 
This  suggests  that  the  temperature  variation  is  due  to  a  change  in  a 
physiological  factor  different  from  that  involved  in  the  age  variation; 
and  that  probably  it  is  due  to  a  modification  of  the  coefficient  of  cross- 
ing-over of  the  chromosome  itself. 


200  THE    SECOND-CHROMOSOME    GROUP 

STRAP  (V). 

(Plate  8,  figures  1,  2,  3.) 

ORIGIN  OF  STRAP. 

The  mutation  "strap"  was  found  by  Morgan  about  April  1912,  in 
an  experiment  involving  vestigial  flies.  The  first  individual  (a  female) 
was  regarded  simply  as  a  vestigial  with  extra  long  wings.  The  name 
"strap"  was  given  because  of  the  extreme  narrowness  of  the  wings. 
As  in  the  case  of  vestigial,  they  extend  laterally  from  the  body,  though 
not  quite  as  nearly  at  right  angles  as  are  the  wings  of  vestigial. 

INHERITANCE  OF  STRAP. 

The  first  female  was  bred  to  a  vestigial  brother  and  produced  in  Fi 
all  vestigial  offspring.  In  F2,  however,  the  strap-winged  type  reap- 
peared in  about  a  quarter  of  the  individuals,  showing  that  strap  was 
not  simply  a  "long"  vestigial,  but  that  there  had  been  a  distinct 
mutation.  That  the  mutation  was  not  sex-linked  was  evident  from 
the  Fi  result,  since  the  sons  of  the  strap  female  had  failed  to  show  the 
strap  character. 

STOCK  OF  STRAP. 

Some  of  these  Fo  strap  individuals  were  inbred  and  gave  a  stock 
practically  all  of  which  were  "strap."  Selection  was  practiced  for 
many  generations  to  increase  the  length  and  narrowness  of  the  wings, 
but  WTithout  success  further  than  to  establish  a  homogeneous  stock,  in 
which  every  individual  was  typically  strap. 

DESCRIPTION  OF  STRAP. 

While  there  is  considerable  variation  in  the  character,  the  wing  is 
always  found  to  be  longer  than  vestigial.  The  tip  of  the  wing  is 
narrow  and  elongated,  while  the  base  is  broader  than  vestigial,  espe- 
cially on  the  inner  (rear)  margin,  so  that  the  whole  wing  often  has  a 
"leg-o'-mutton"  appearance.  The  venation  is  normal;  that  is,  the 
bases  of  all  the  longitudinal  veins  are  present  and  usually  nearly  all 
of  the  second  longitudinal  vein  which  runs  out  along  the  narrow  tip 
either  near  or  at  its  outer  (forward) margin.  The  rest  of  the  venation  is 
cut  away  along  with  the  blade  of  the  wing  The  balancers  are  affected 
in  an  analogous  manner,  the  terminal  segment  being  much  reduced, 
though  probably  never  gone,  as  it  often  is  in  vestigial.  A  curious 
correlation  noted  is  that  the  more  of  the  wing-blade  there  is  present 
the  larger  is  this  terminal  segment  of  the  balancer  and  also  the  closer 
to  normal  is  the  position  of  the  wing.  _ , 

I 


PLATE  8 


OF    MUTANT    CHARACTERS. 


CHROMOSOME  CARRYING  STRAP. 


201 


The  view  of  strap  prevalent  at  that  time  was  that  it  was  vesti^nal 
modified  in  the  direction  of  the  wild  form  by  a  recessive  autosomal 
modifier.  On  this  assumption  it  was  expected  that  in  crosses  to  wild 
there  would  be  produced  in  F2  vestigials  as  well  as  straps,  and  also 
some  flies  having  the  modifier  only.  It  was  problematical  wlmt 
these  latter  flies  should  look  like,  though  in  general  it  was  expected 
that  they  might  have  longer  wings  than  normal,  just  as  strap  wiis 
larger  than  vestigial.  In  F2,  however,  no  vestigial  appeared  and  the 
only  certain  classes  were  the  wild-type  and  the  strap  flies  in  the  usual 
3 : 1  ratio.  It  is  true  that  a  few  of  the  flies  were  vestigial-like,  but  none 
were  typical  vestigials,  and  these  intermediate  forms  were  regarded  as 
fluctuations  of  strap. 

One  of  these  vestigial-like  straps  was  crossed  out  to  wild  and  8  F2 
cultures  were  raised.  Among  the  940  F2  ofifspring  there  were  only  20 
that  repeated  the  vestigial-like  appearance ;  the  remainder  (175)  of  the 
strap  flies  graded  from  this  shortest  type  through  the  usual  range  of  strap. 

The  F2  (table  46)  from  the  cross  of  strap  to  black  gave  a  typical 
2:1:1:0  ratio,  which  showed  that  strap  was  in  the  second  chromosome, 
as  had  been  concluded  from  the  failure  of  vestigials  to  appear  in  the 
former  F2.  There  was  here  also  no  apparent  crossing-over  between 
vestigial  and  a  possible  vestigial  modifier  responsible  for  strap. 

Table  46. — Pi,  strap  9   X  hlack  cT;  Fi  wild-type  9  -\-  Fi  wild-type  cf . 


Apr.  1, 
1914. 

Wild-type. 

Black. 

Strap. 

Black 

strap. 

9 

cf 

9 

cf 

9 

d^ 

9 

0^ 

55.1 

133 

117 

43 

56 

58 

40 

0 

0 

55.2 

72 

68 

28 

39 

25 

30 

0 

0 

55.3 

55 

72 

28 

28 

34 

28 

0 

0 

55.4 

Total .  . 

70 

58 

35 

23 

33 

23 

0 

0 

330 

315 

134 

146 

150 

131 

0 

0 

It  appeared,  then,  either  that  strap  is  vestigial  plus  a  recessive 
modifier  whose  locus  is  very  close  indeed  to  that  of  vestigial,  so  tliat  no 
crossing-over  was  detected  in  the  very  extensive  F2  counts,  or,  more 
probably,  that  strap  is  an  allelomorph  of  vestigial  and  recessive  to  both 
vestigial  and  the  wild-type  allelomorph. 

Quite  recently  several  rather  complicated  experiments  have  been 
attempted  in  an  effort  to  distinguish  between  these  two  alternatives, 
but  with  no  decisive  result.  We  believe,  however,  that  the  whole 
trend  of  the  evidence  in  Drosophila  is  to  the  effect  that  tyj)es  that 
behave  like  strap  and  vestigial  are  examples  of  multiple  allel()m()ri)hism 
and  not  of  close  hnkage.     It  is  probable  that  the  vestigial  system 


202 


THE    SECOND-CHROMOSOME    GROUP 


now  comprises  5  allelomorphs  (wild-type,  vestigial,  strap,  antlered, 
and  nick.) 

That  strap  is  entirely  independent  of  the  third  chromosome  in  its 
inheritance  was  demonstrated  by  an  F2  and  a  back-cross  carried  out 
between  strap  and  pink.  The  F2  ratio  approximated  9  :3  :3  :1,  and 
the  straps  that  were  pink  were  of  the  same  type  as  those  that  were  not. 

The  back-cross  test  of  Fi  males  (table  47)  gave  1,063  flies,  of  which 
534  were  recombinations.  This  is  a  percentage  of  50.2,  where  50.0  was 
expected,  with  free  assortment  between  different  chromosomes. 

Table  47. — Pi,  strap  9  X  pink  cf ;  Fi  wild-type  9  hack-crossed 

hy  strap  pink  cf . 


June  25,  1913. 

Strap. 

Pink. 

Strap  pink. 

Wild-type. 

M  38 

44 
60 

58 
84 

50 

78 
66 
89 

37 
68 
54 
83 

56 
92 

58 
86 

M38r 

M  39 

M  39r 

Total... 

246 

283 

242 

292 

The  character  strap  has  never  been  used  in  new  linkage  experiments, 
since  vestigial  answers  as  well  in  this  regard,  and  the  strap  wing  is  not 
quite  large  enough  to  permit  the  simultaneous  use  of  such  other  wing 
and  venation  characters  as  curved,  arc,  plexus,  etc. 

ARC  (a). 

(Plate  7,  figure  4.) 

ORIGIN  OF  ARC. 

A  stock  of  flies  was  being  looked  over  by  Bridges  in  search  of  indi- 
viduals with  black  palpi,  which  were  occasionally  produced,  when  it 
was  noticed  that  roughly  10  per  cent  of  the  flies  were  showing  a  new 
wing-character  (culture  B  30,  May  24,  1912). 

DESCRIPTION  OF  ARC. 

This  character  was  called  "arc,"  since  the  wing  was  bent  downward 
in  an  even  curve  from  base  to  tip,  and  also  from  side  to  side.  The 
margins  tend  to  roll  slightly  in  diagonal  lines,  so  that  the  wing  ap- 
proaches a  diamond-shape.  The  w^ing  is  somewhat  broader  than 
normal.  The  texture  of  the  wing  is  only  slightly  thinner  than  normal. 
Usually  the  wings  diverge  sUghtly,  and  occasionally  tilt  over  to  the 
side,  giving  the  appearance  of  a  droop  to  the  outer  edge.  As  far  as 
can  be  seen,  the  character  is  restricted  entirely  to  these  wing  changes. 


OF    MUTANT    CHARACTERS. 


203 


STOCK  OF  ARC. 

The  character  arc  had  appeared  in  females  as  well  as  nuiles,  so 
that  material  was  on  hand  to  establish  a  stock.  A  mass-culture 
produced  a  stock  that  seemed  to  be  pure.  Several  pair  matings  made 
at  the  same  time  proved  completely  fertile,  and  from  one  of  these  a 
permanent  stock  was  started. 

INHERITANCE  OF  ARC. 

In  crosses  of  arc  to  wild  all  the  Fi  flies  were  wild-type,  showing  that 
arc  is  recessive.  Three  mass-cultures  and  two  pairs  of  Fi  flics  ga\'e  a 
total  of  2,596  offspring,  of  which  648  or  24.8  per  cent  were  arcs  (table  48). 

Table  48.— Pi,  arc  9  9  X  ivild  d^d';  Fi  mid-type  9  9  X  Fi  wild-type  dd. 


Aug.  5,1912. 

Wild-type. 

Arc. 

B  6.3 

B64 

B65 

B66 

B67 

Total .... 

528 
390 
509 

272 
249 

205 
126 
167 

89 
61 

1,948 

648 

EPIDEMIC  OF  ARCS. 

Just  as  in  the  cases  of  purple  and  of  jaunty,  there  was  a  short  period 
following  the  discovery  of  arc  during  which  arcs  appeared  and  in  the 
most  diverse  stocks.  Within  6  months  9  other  appearances  of  arcs 
had  been  recorded  by  Bridges  (table  47).  Of  these,  arc  8  proved  to 
be  sex-linked  (bow),  and  at  least  2  others  were  not  arc  itself,  since 
when  bred  to  arc  they  gave  straight  wings.  Arcs  7  and  9  were  the 
same  as  (or  at  least  allelomorphic  to)  the  original  arc.  Both  of  these 
occurred  in  distinct  stocks  and  were  probably  independent  appear- 
ances.    Cultures  B  66  and  B  67  (table  48)  are  F2's  from  arc  7  by  wild. 

CHROMOSOME  CARRYING  ARC. 

At  this  time  (June  1912)  the  autosome  groups  were  still  very  nebu- 
lous. The  "second"  group  was  slowly  condensing  around  black,  but 
so  far  as  recognized  comprised  only  black,  curved,  purple,  and  vestigial, 
though  other  mutants  had  been  found  which  later  evidence  showed 
were  second  chromosome.  The  key  tests  had  not  yet  been  made 
w^hich  linked  all  of  these  into  a  solid  system.  The  third  chromosome 
group  was  in  far  worse  plight,  being  defined  simply  b}^  pink.  It  was 
for  this  reason  that  in  testing  the  chromosome  of  arc  some  exiicrinicnts 
were  made  that  would  now  be  useless.  For  example,  arc  was  crossed 
to  pink  and  gave  in  F2  a  close  approach  to  a  9  :3  :3  : 1  ratio  (table  49). 


1 


204 


THE    SECOND-CHROMOSOME    GROUP 


The  presence  of  the  double  recessive  arc  pink  in  the  F2  of  the 
"repulsion"  cross  would  now  be  regarded  as  conclusive  proof  that 
arc  was  not  third-chromosome;  but  at  that  time  the  fact  that  there  is 
no  crossing-over  in  the  male  had  not  yet  been  discovered,  and  the 
above  result  meant  to  us  either  free  crossing-over  or  separate  chromo- 
somes. Only  further  tests  could  decide  which  of  these  alternatives 
was  correct.  There  were  still  other  reasons  for  further  tests.  At  this 
early  period  it  was  important  to  prove  to  the  satisfaction  of  everybody 
that  if  a  new  mutation  showed  linkage  to  any  one  member  of  a  group 

Table  49. — Pi,  pink  9    X  arc  cT ;  Fi  wild-type  9  9 
+  Fi  wild-type  cf  cf . 


July   11,   1912. 

Wild-type. 

Arc. 

Pink. 

Arc  pink. 

B  46 

260 
112 
201 
102 

104 
27 
49 
31 

100 
71 
58 
30 

36 
21 

27 
13 

B  47 

B  48 

B  49 

Total 

675 

211 

259 

97 

it  must  show  linkage  to  every  member,  even  though  in  some  cases 
this  linkage  be  very  slight  because  of  the  long  distance  between  the 
loci.  Conversely,  if  a  mutant  failed  to  show  linkage  to  one  member 
of  a  group  it  was  still  necessary  to  show  that  it  would  likewise  fail  to 
show  linkage  to  other  members.  For  this  reason  arc  had  been  crossed 
to  maroon  at  the  same  time  as  to  pink.     It  is  true  that  it  was  not  then 

Table  50. — Pi,  arc  9  X  maroon  d^;  B.C.,  Fi  wild-type  9  9  X 

arc  maroon  cf  cf . 


July  31,  1912. 

Arc. 

Maroon. 

Arc  maroon. 

Wild-type. 

B  60 

214 
230 
260 

209 
204 
231 

247 
206 
266 

195 
211 
255 

B  61 

B  62 

Total 

704 

644 

719 

661 

definitely  known  that  maroon  was  third-chromosome,  but  it  was  seen 
that  these  tests  would  determine  to  which  chromosome  maroon  be- 
longed. The  arc-maroon  ''repulsion"  likewise  gave  an  approach  to  a 
9  :3  :3  :1  ratio.     (Culture  B  50;  +  158,  a  54,  m,  41,  a  m^  20.) 

To  make  more  certain  that  no  appreciable  linkage  was  present, 
three  back-cross  cultures  were  made  (table  50). 

In  the  total  of  2,728  flies  of  this  arc  maroon  back-cross  there  were 
1,348,  or  49.05  per  cent  of  recombinations,  where  50.0  is  expected 
from  free  assortment. 


OF   MUTANT    CHARACTERS. 


205 


The  independence  shown  in  the  arc  pink  and  arc  maroon  crosses 
was  interpreted  to  mean  that  arc  was  in  a  separate  chromosome  from 
these  two  and  therefore  probably  in  the  second  chromosome.  Tliat 
this  was  the  case  was  proved  by  the  result  of  the  cross  of  arc  by  black, 
which  produced  in  F2  no  double-recessive  black  arc  (table  51). 

Table  51. — Pi,  arc  9    X  black  cf ;    Fi  ivild-type  9  9    X 

Fi  wild-type  d*  cf . 


July  10,  1912. 

Wild-type. 

Black. 

Arc. 

Black  arc. 

B  42 

314 
1:34 
145 
94 
236 

130 
62 
59 
51 
99 

152 
48 
45 
49 
93 

0 
0 
0 
0 
0 

B  4:3 

B  44 

B  45 

B45.1 

Total 

923 

401 

387 

0 

While  this  result  was  accepted  as  providing  that  arc  was  linked  to 
black  and  was  therefore  second-chromosome,  it  was  not  regarded  as 
proving  absolute  linkage  of  black  and  arc,  but  merely  linkage  so  close 
that  two  cross-over  gametes  had  not  chanced  to  meet.  The  correct 
interpretation  that  the  2:1:1:0  was  the  result  of  no  crossing-over 
in  the  male  was  not  suspected ;  however,  it  was  considered  remarkable 
that  all  the  autosomal  Unkages  thus  far  encountered  had  been  so 
extreme. 

LOCUS  OF  ARC. 

In  order  to  conduct  a  back-cross  test  of  the  amount  of  crossing-over 
between  black  and  arc  it  was  necessary  to  obtain  the  double  recessive 
black  arc.  By  accident  the  most  advantageous  method  was  used, 
namely,  F2  blacks  and  F2  arcs  were  mated  together.  Several  mass- 
cultures  of  this  sort  were  started  from  B  42  and  fortunately  black 
arc  flies  appeared  in  F3.     From  these  a  pure  stock  was  made. 

The  actual  back-cross  test  was  not  carried  out  for  some  months; 
meanwhile  the  black  vestigial  back-crosses  had  demonstrated  that  in 
that  case  at  least  there  was  no  crossing-over  in  the  miile.  It  was 
necessary  to  test  this  fact  by  other  cases,  since  the  purple  vestigial 
back-cross  had  previously  given  a  few  apparent  cross-overs  in  the  male. 
"CoupUng"  back-cross  tests  of  the  female  and  of  the  male  were  there- 
fore started  at  the  same  time  from  the  mating  of  black  arc  male  to 
wild  female.  The  test  of  the  male  furnished  306  flies,  every  one  of 
which  was  a  non-crossover  (table  52) . 

The  result  of  the  male  test  was  particularly  striking  in  view  of  the  very 
free  crossing-over  shown  by  the  parallel  tests  of  the  female  (table  53). 

In  the  female  tests  there  was  a  total  of  798  flies,  of  which  2SG  or 
35.9  per  cent  were  cross-overs. 


206 


THE    SECOND-CHROMOSOME    GROUP 


It  was  assumed  without  question  that  arc  was  in  the  same  direction 
from  black  as  were  purple  and  vestigial,  the  only  three  genes  previously 
mapped.  Arc  and  vestigial  do  not  make  a  classifiable  combination, 
so  that  it  was  not  advisable  to  test  further  the  locus  of  arc  by  means 
of  the  vestigial-arc  back-cross;  but  purple  and  arc  are  workable  and 
accordingly  the  purple  arc  double  recessive  was  made  up.  By  this 
time,  however  (April  1913),  curved  and  speck  had  been  mapped,  and 
the  position  of  speck  was  seen  to  be  close  to  the  assumed  position  of  arc, 
but  even  farther  away  from  black,  since  black  speck  gave  about  49 
per  cent  of  crossing-over  as  against  the  36  given  by  black  arc.  It  was 
resolved  to  run  a  three-point  experiment,  using  speck  as  well  as  purple 
and  arc.  The  first  step  in  this  was  to  get  arc  and  speck  together, 
which  proved  a  troublesome  job.  The  difficulty  lay  solely  in  the  fact 
that  the  loci  of  these  two  are  so  close  together  that  only  rarely  was  one 

Table  52. — Pi,  black  arc  cf   X  wild  9 ;  B.  C,  F^  wild-type  cf   X 

stock  black  arc  9  9  . 


Dec.  18,  1912. 

Black  arc. 

Wild-type. 

Black. 

Arc. 

II  5 

145 

161 

0 

0 

of  the  F2  arcs  or  F2  specks  a  cross-over,  and  the  first  two  attempts 
failed.  The  double  was  finally  obtained  (October  1913).  It  was  now 
an  easy  matter  to  obtain  the  purple  arc  speck  triple  recessive  (F3  from 
the  cross  of  purple  arc  by  arc  speck). 


Table  53. — Pi,  black  arc  cf   X  wild  9 ;  B.  C,  Fi  wild-type  9 

stock  black-arc  cf  cf . 


X 


Dec.  13,  1912. 

Black  arc. 

Wild-type. 

Black. 

Arc. 

C  172 

122 
101 

190 
99 

67 
69 

84 
66 

113 

Total 

223 

289 

136 

150 

The  Pi  for  the  back-cross  was  made  by  mating  a  purple  female  to  an 
arc  speck  male,  which  was  considered  a  better  type  of  mating,  from 
the  standpoint  of  viabiHty,  than  to  have  all  the  mutants  enter  from 
one  parent. 

The  back-cross  (table  54)  furnished  2,625  flies,  of  which  1,431  were 
non-cross-overs,  1,038  cross-overs  between  purple  and  arc,  128  cross- 
overs between  arc  and  speck,  and  28  cross-overs  in  both  regions  at 
once.  The  distance  of  arc  from  purple  was  found  to  be  greater  than 
first  indicated  by  the  black  arc  value  (36),  since  now  40.6  per  cent  of 
crossing-over  was  observed.     This  longer  distance  is  in  better  agree- 


OF    MUTANT    CHARACTERS. 


207 


ment  with  the  black  speck  value  and  with  the  short  arc  speck  value 
found. 

The  coincidence  corresponding  to  these  data  is  44.2,  calculated  as 
follows : 

2625  X  28  X  100 
(1038  +  28)  X  (128  +  28)  "  ^^'^ 

This  coincidence,  as  compared  with  the  coincidences  found  for  the 
other  cases  involving  the  region  around  black,  purple,  vestiguil,  and 
curved,  were  surprisingly  low,  and  suggested  that  the  coincidences 
involving  the  right  end  were  different  from  those  involving  the  part 
then  regarded  as  the  left  end,  but  now  regarded  as  the  middle  of  the 
chromosome. 

There  is  one  other  important  linkage  experiment  involving  arc, 
namely,  the  black  arc  morula  back-crosses  with  balanced  inviabiUty. 
These  crosses,  which  furnished  a  total  of  6,794  flies  (table  84),  are 
treated  under  the  section  on  morula. 

Table  54. — Pi,  purple   9    X  arc  speck  cf;  B.  C,  Fi  wild-type    9   X  stock 

purple  arc  speck  cf . 


Oct.  24,  1914. 

Pr 

Pr       1 

a    Sp 

Pr 

1  Sp 

Pr 

1 

1  «p 

Total. 

a      Sp 

1 

a 

Purple. 

Arc 
speck. 

Purple 

arc 
speck. 

Wild- 
type. 

Purple 
speck. 

Arc. 

Purple 
arc. 

Speck. 

637 

67 
35 
89 
36 
99 
69 
94 
118 
41 
92 

68 
32 
89 
34 
111 
71 
77 
82 
34 
93 

47 
29 
44 
19 
66 
52 
67 
54 
32 
68 

56 
44 
59 
37 
74 
68 
62 
60 
31 
69 

3 
4 
6 
3 

13 
7 
9 

10 
2 

4 

6 
2 
9 
4 
5 
6 

13 
5 
1 

10 

3 

2 

252 
146 
299 
137 
370 
279 
326 
335 
144 
337 

638 

639 

680 

1 

1 
3 

3 
3 
2 

5 
1 

681 

682 

683 

684 

685 

686 

Total 

1 

1 

2 

740 

691 

478 

560 

67 

61 

10 

18 

2,625 

Table  55. — Summary  of  all  linkage  data  involving  arc. 


Loci. 

Total. 

Cross-overs. 

P.  ct. 

Date. 

Source. 

Black  arc. . 

Purple  arc . . 
Arc  speck. . . 
Arc  morula. 

'     798 
6,794 

286 
2,951 

35.9 
43.4 

Dec.  13,  1912 
Aug.    4,  1914 

Oct.   24,  1914 
Oct.   24,  1914 
Aug.    4.  1914 

Bridges;  6  a  X  wild  B.  C;  C172. 

IL  3. 
Bridges;  b  a  rrif  balanced  B.  C; 

364. 

Bridges;  Pr  X  a  »p  B.  C;  37-686. 
Bridges;  /»,  X  a  sp  B.  C. ;  637-686. 
Bridges;  b  a  nXf  balanced  B.  C; 
364. 

7,592 

3,237 

42.6 

2,625 
2,625 
6,794 

1,066 
156 
534 

40.6 
5.9 
7.9 

208  THE    SECOND-CHROMOSOME    GROUP 

A  summary  of  the  linkage  data  involving  arc  is  given  in  table  55. 
The  locus  of  arc  on  the  basis  of  these  data  is  6.7  units  to  the  left  of 
speck,  which  is  its  base  of  reference,  or  98.4  units  from  star. 

The  calculation  of  the  locus  of  arc  made  by  Muller  (1916)  on  the 
basis  of  relatively  few  flies  agreed  with  this  position. 

VALUATION  OF  ARC. 

Arc  is  of  second  rank  as  a  working  character;  its  demerit  comes  from 
the  fact  that  the  character  is  occasionally  simulated  in  the  wings  of 
flies  of  not-arc  stocks.  The  occurrence  of  such  mimics  in  a  critical 
experiment  involving  arc  would  lead  to  confusion  in  the  classification 
and  to  seemingly  impossible  results.  The  opposite  error — failure  to 
distinguish  the  character  in  flies  really  arc — occurs  rarely  or  possibly 
never.  In  all  other  respects  arc  is  of  first  rank;  in  viability  and  habit 
it  is  excellent;  its  locus  is  especially  convenient,  since  it  is  situated  in 
the  gap  between  curved  and  speck  near  the  right  end  of  the  known 
chromosome,  and  since  the  arc-speck  interval  of  5.9  is,  like  black 
purple,  long  enough  to  avoid  the  high  probable  errors  due  to  small 
percentages  of  crossing-over,  but  short  enough  to  avoid  all  danger  of 
double  crossing-over  within  it,  and  likewise  to  afford  a  concise  "  caliper" 
region  in  studies  on  coincidence  or  linkage. 

GAP. 

(Text-figure  76.) 

ORIGIN  OF  GAP. 

The  first  appearance  of  the  character  called  "gap  "  was  in  an Fi mass- 
culture  from  the  cross  of  black  by  arc  (July  10,  1912,  culture  B  42, 
table  51).  Several  of  the  black  flies  of  that  culture  showed  a  break 
or  gap  in  the  fourth  longitudinal  vein  between  the  posterior  cross-vein 
and  the  wing-tip.  This  gap  varied  from  nearly  all  of  this  section  (see 
fig.  76)  to  a  mere  weakening  of  the  vein.  The  black  color,  which  nor- 
mally in  black  flies  forms  a  heavy  band  on  each  side  of  the  veins,  was 
likewise  absent  from  this  region.  From  B  42  the  stock  of  black  arc 
was  derived,  and  this  stock  occasionally  showed  the  gap  character. 
Little  attention  was  paid  to  it  until  it  turned  up  again  in  a  cross 
involving  black  arc  (March  19,  1913). 

INHERITANCE  OF  GAP. 

A  gap  black  arc  female  was  then  crossed  back  to  a  stock  black  arc 
male  which  did  not  show  gap.  In  Fi  there  appeared  27  gap  to  55  not- 
gap  offspring  (M  37).  It  was  not  known  whether  this  denoted  that 
the  male  had  been  heterozygous  for  gap,  which  is  recessive,  or  that  the 
gap  character  was  dominant.  In  either  case  the  character  gave  little 
promise  of  usefulness,  since  obviously  some  of  the  flies  really  gap  were 


OF   MUTANT    CHARACTERS.  209 

failing  to  show  the  character.  Such  a  character  can  be  used,  though 
very  inefficiently,  by  considering  those  flies  which  do  show  the  charac- 
ter and  disregarding  the  majority  which  do  not. 

That  gap  is  recessive  was  indicated  by  the  mating  carried  out  when 
gap  reappeared  in  still  another  experiment  (May  27,  1913).  A  gap 
(black  arc)  female  out-crossed  to  a  wild  male  gave  only  not-gap  off- 
spring (Culture  II  38,  +  9  51,  X  cf  63).  On  the  other  hand,  another 
such  female  out-crossed  to  a  black  male  gave  in  Fi  38  gap  to  65  not-gap 
offspring  (II  41).  This  seemed  to  indicate  dominance,  since  the  bkick 
stock  had  been  examined  several  times  and  no  gaps  had  been  found. 
In  addition,  several  of  the  gap  males  and  females  were  bred  together, 
and  these  produced  a  stock  which  seemed  pure,  since  in  every  fly  at 
least  a  weakening  of  the  vein  and  color  could  be  seen,  while  fully  90 
per  cent  showed  a  distinct  and  large  gap.  The  stock  maintained  this 
condition  when  run  without  selection,  while  at  the  same  time  the 


Text-figure  76. — Gap  venation,  showing  the  break  in  the  fourth  longitudinal  vein. 

regular  black  and  black  arc  stocks  failed  to  show  gap  when  examined 
occasionally.  It  now  seemed  probable  that  there  might  be  some 
special  relation  operative  in  the  case  of  gap  to  account  for  the  apparent 
dominance  when  crossed  to  black  or  black-arc  and  the  recessiveness 
when  crossed  to  wild.  About  a  year  later  (July  1914)  the  cross  of 
gap  black  arc  to  black  arc  was  repeated,  whereupon  the  same  domi- 
nance reappeared  in  the  case  of  two  tests  out  of  the  three  (table  56). 
Some  of  these  Fi  gap  males  were  in  turn  crossed  back  to  black-arc 
females  from  stock,  with  the  result  that  only  a  very  small  percentage 
of  the  offspring  showed  gap  (table  56).  IMost  of  these  gaps  were 
females  and  all  showed  the  character  very  weakly.  This  result  was  in 
sharp  contrast  to  the  Fi  result,  where  the  gap  cliaracter  was  well 
developed,  and  appeared  in  fully  half  the  flies,  about  equally  in  males 
and  females. 

A  not-gap  Fi  black  arc  male  similarly  back-crossed  to  a  black  arc 
female  of  stock  failed  to  give  any  gap  in  123  flies.  This  may  indicate 
a  genetic  difference  between  the  gap  and  not-gap  P^  flies.  An  F2 
culture  raised  from  a  gap  female  and  a  not-gap  male  showed  35  strongly 


i 


210 


THE   SECOND-CHROMOSOME    GROUP 


developed  gaps  in  a  total  of  115  flies,  or  30  per  cent.  If  the  gap  Fi 
mother  had  been  homozygous  for  gap  and  the  not-gap  father  heter- 
ozygous, 50  per  cent  of  gap  offspring  would  have  been  expected. 
Cultures  M  37,  II  41,  and  397  each  gave  very  nearly  a  2  not-gap  to  1 
gap  ratio.     Their  total  was  exactly  200  not-gap  to  100  gap. 

No  satisfactory  conclusion  has  been  drawn  from  these  data,  though  on 
the  whole,  gap  seems  to  be  a  recessive  character,  and  there  is  probably 
present  in  the  original  black-arc  stock  some  special  modifier  or  rela- 
tionship that  makes  gap  appear  in  the  Fi  of  the  cross.  There  seems 
also  to  be  a  sex-limited  or  sex-linked  difference. 

The  gap  stock  is  still  (April  1918)  on  hand  and  shows  the  same 
condition  of  the  character  after  5  years  of  unselected  culture. 

Table  56. — Pi,  gap  black  arc  9    X  black  arc  cf . 


July  18,  1914. 

Black 
arc  9 . 

Black 
arc  c?. 

Gap  black 
arc  9 . 

Gap  black 
arc  cf. 

304 

15 
14 
10 

8 

3 

19 

13 
12 

9 
10 

305 

306 

Fi  gap  black  arc  d'  X  black  arc  9  of  stock. 

350 

59 

42 

59 

125 

81 

56 

48 

59 

136 

103 

358 

9 

7 
4 
3 

1 
1 

359 

381 

382 

Fi  not-gap  black  arc  cf  X  black  arc  9  of  stock. 

360 

55 

68 

Fi  gap  black  arc  9   +  Fi  not-gap  black  arc  d^. 

397 

80 

35 

CHROMOSOME  AND  LOCUS  OF  GAP. 

The  evidence  that  gap  is  second-chromosome  consists  solely  in  the 
persistence  with  which  gap  has  accompanied  black  through  certain 
crosses.  The  fact  that  a  cross-over  between  black  and  gap  in  getting 
black  arc  stock  retained  gap  with  the  black  suggests  that  the  locus  of  | 
gap  is  to  the  left  of  arc  and  perhaps  near  curved. 


4 


OF    MUTANT    CHARACTERS.  211 

ANTLERED  (vt)- 

(Plnte  <).) 

ORIGIN  OP  ANTLERED. 

The  character  "antlered"  was  found  by  Alorgan  about  September 
1912,  and  a  pure  stock  was  secured.  It  seems  to  have  originated  in 
an  experiment  involving  vestigial. 

DESCRIPTION  OF  ANTLERED. 

The  wings  of  antlered  flies  are  on  the  average  longer  than  those  of 
strap,  often,  indeed,  being  full  length.  The  wing  is  also  broader  in 
the  distal  portion,  so  that  sometimes  it  can  scarcely  be  distinguished 
in  form  from  a  rather  extreme  beaded.  Like  strap,  too,  the  wings  are 
held  out  at  rather  wide  angles  (about  30°  from  the  axis  of  the  body). 
A  unique  feature  of  antlered  is  that  the  long  type  of  wing  is  quite  often 
folded  at  the  tip  (see  fig.  2,  plate  9). 

INHERITANCE  OF  ANTLERED. 

Rather  extensive  breeding  and  selection  experiments  were  carried 
out  on  this  wing,  the  records  of  which  have  been  lost.  The  results, 
however,  were  in  agreement  with  some  later  data,  which  may  be 
given.  Antlered  males  out-crossed  to  wild  females  gave  wild-type 
Fi  offspring.  Seventeen  mass-cultures  of  the  Fi  flies  were  bred,  gi\'ing 
in  F2  a  total  of  5,234  flies,  of  which  1,036  or  19.8  per  cent  were  antlered 
(August  1915;  Morgan,  1915,  p.  10).  That  is,  antlered  is  a  simple 
recessive  to  wild,  and  the  F2  ratio  was  aberrant  because  of  the  crowding 

Table  57. — Pi,  antlered  cf  cf   X  vestigial  9  9.     Fi  vestigial  9  9    -f-  Fi 

vestigial?  cf  cf. 


March  4,  1913. 

Vestigial  9 . 

Antlered  9 . 

Vestigial  cf. 

Antlered  cT. 

No.  25 

87 

36 

37 

80 

28 

175 

48 

96 

60 

28.1 

249 

38 

186 

62 

30 

191 

13 

113 

43 

31 

63 

42 

15 

72 

33 

132 

12 

100 

50 

34 

183 

64 

103 

135 

35 

Total 

191 

64 

81 

80 

1,271 

317 

731 

682 

that  always  takes  place  in  mass-cultures.  The  antlered  did  not  split 
up  in  F2,  which  shows  that  antlered  is  not  vestigLal  plus  a  modifier 
unless  that  modifier  is  in  the  second  chromosome  linked  so  closely  to 
vestigial  that  no  appreciable  crossing-over  occurred. 

^Vhen  antlered  males  were  crossed  to  vestigial  females  the  Fi  flies 
were  not  wild-type.     They  are  recorded  as  being  all  vestigial  (Feb- 


212 


THE   SECOND-CHROMOSOME    GROUP 


ruary  8,  1913;  Bridges,  p.  35),  but  this  is  probably  incorrect  in  view  of 
all  other  results.  No  counts  were  made,  or  it  would  probably  have 
been  noticed  that  some  at  least  of  the  Fi  flies  were  more  like  antlered 
than  vestigial. 

Eight  Fo  mass-cultures  were  raised  (table  57),  and  these  produced 
a  total  of  2,901  flies,  of  which  899  or  31.0  per  cent  were  antlered.  On 
the  basis  that  antlered  is  completely  recessive  to  vestigial,  only  25 
per  cent  of  the  flies  should  have  been  antlered;  that  is,  twice  (31—25) 
or  12  per  cent  of  the  vestigial-antlered  compounds  were  more  like 
antlered  than  vestigial. 

An  examination  of  the  F2  counts  showed  that  antlered  dominated 
in  the  males  but  not  in  the  females.  The  antlered  males  comprised 
44.3  per  cent  of  all  the  males,  which  means  that  at  least  38.6  per  cent 

Table  58. — Pi,  antlered  9    X  vestigial  d'. 


March  26.  1913. 

Vestigial  9  • 

Antlered  9 . 

Vestigial  cf . 

Antlered  cf . 

39 

92 

78 

130 

57 

28 
69 

36 
40 
25 

39  1         .      ... 

40 

Total 

300 

154 

101 

Fi  vestigial  9  9  +  Fi  vestigial  cf  cf . 

40.1 

266 
211 
98 
56 
150 
178 

104 
66 
33 
15 
42 
61 

187 
146 
68 
31 
108 
184 

211 

109 

52 

18 
77 
79 

41.1 

41.2 

41.3 

41.4 

42 

Total 

959 

321 

724 

546 

of  the  vestigial-antlered  compound  males  were  antler-like.  Among 
the  females  only  20  per  cent  were  antler-like,  which  probably  means 
that  the  composition  in  mass-culture  had  lowered  the  percentage  of 
antlered  females  from  25  to  20,  just  as  in  the  F  2  from  antlered  by  wild 
the  percentage  of  antlered  was  only  19.8. 

The  reciprocal  cross  (antlered  9  X  vestigial  cf)  was  started  about 
two  months  later  than  the  cross  just  described,  and  here  more  attention 
was  paid  to  the  nature  of  the  Fi  flies  (table  58). 

The  relation  deduced  from  the  previous  F2  was  observed  in  the  new 
Fi ;  for  while  none  or  only  very  few  of  the  Fi  females  were  antlered-like, 
36.9  per  cent  of  the  males  were  antlered.  These  antlered- vestigial 
compounds  were  not  typical  antlered,  but  were  shorter  and  very  much 
like  strap. 

Six  Fi  mass-cultures  gave  in  F2  a  total  of  1,280  females,  of  which  321 
or  25.1  per  cent  were  antlered,  and  1,270  males,  of  which  546  or  43.0 


PLATE  9 


OF   MUTANT   CHARACTERS. 


213 


per  cent  were  antlered  and  antlered-like.  That  is,  about  36  per  cent 
of  the  vestigial-antlered  compound  niales  were  longer  than  vestigial 
(table  58).  The  percentage  of  antlered  dominance  in  F^  (3(3  per  cent) 
was  the  same  as  that  observed  in  Fi  (36.9  per  cent). 

One  other  experiment  was  made  in  1913  and  repeated  in  1915, 
namely,  the  cross  of  antlered  male  to  black  vestigial  female  carried  to 
F2  (table  59).  In  the  Fi  females  there  was  a  slight  amount  of  antlered 
dominance  (6  per  cent)  and  among  the  males  very  much  more  (57 
per  cent). 

Table  59. — Pi,  antlered  cf  X  black  vestigial  9  . 


March  22,  1913. 

Vestigial  9 . 

Antlered  9 . 

Vestigial  d'. 

Antlered  d'. 

II  43 

158 
117 

10 

7 

54 

52 

84 
57 

II  47 

Total 

275 

17 

106 

141 

Fi  vestigial  9   +  Fi  antlered  cf . 

bvg  9. 

Vg"    9. 

bVg"     9. 

Vg    9. 

bvgd". 

vo'^d'. 

b  Vg"  cT. 

Vt<^. 

II  47.1 

94 
452 

102 
596 

2 

48 

164 
648 

92 
371 

145 
767 

8 
74 

109 
269 

1915,  6  +  17.1 

^al 

546 

69S 

50 

812 

463 

912 

82 

378 

Th3  Fo  cultures  raised  in  1913  agreed  closely  with  the  classification 
of  2c  pair  cultures  made  in  1915  by  ]M organ.  Together  these  Fo 
cultures  gave  3,941  flies,  of  which  1,742  or  44.2  per  cent  were  antlered 
or  aiitlered-like.  That  is,  besides  the  homozygous  antlered,  38.4  per 
cent  of  the  vestigial-antlered  compounds  could  be  separated  from  the 
vestigials,  though  not  from  the  antlered.  Among  the  females  the  ant- 
lered dominance  was  23  per  cent  and  among  the  males  58  per  cent, 
which  is  in  agreement  with  the  57  per  cent  observed  in  the  Fi  males. 

A  rough  calculation  of  the  amount  of  crossing-over  between  black 
and  antlered  was  made,  as  follows:  There  were  in  the  experiment  44.2 
per  cent  of  antlered  flies  where  only  25  per  cent  would  have  been  expect- 
ed if  antlered  were  a  strict  recessive.  That  is,  19.2  per  cent  (44.2  —  25)  of 
all  the  flies  (3,941)  or  757  flies  were  due  to  antlered  dominance.  There 
were  132  black  antlered  flies,  all  of  which  were  due  to  antlered  domi- 
nance and  all  of  which  were  cross-overs  between  black  and  antlered. 
In  the  total  of  757  comparable  flies,  132  or  17.4  per  cent  were  cross- 
overs, which  agrees  remarkably  with  the  mapped  black  vestigial 
distance  of  17.5. 

Just  as  in  the  case  of  strap,  all  the  data  point  to  the  allel(Mnorphism 
of  antlered  to  vestigial.     The  vestigial-antlered  compound  is  in  the 


214 


THE    SECOND-CHROMOSOME   GROUP 


Thht-pigure  77. — Vestigial-an tiered  compounds.     Fig.  776  shows  the  compound  male,  wbich 
usually  has  a  longer  wing  than  the  corresponding  female,  fig.  77  a. 

female  indistinguishable  from  pure  vestigial  in  fully  90  per  cent  of  the 
flies,  and  in  the  remainder  is  intermediate  in  type  (fig.  77,  a),  and  while 
distinguishable  from  pure  vestigial,  grades  off  toward  the  pure  ant- 
lered  type.  In  the  males  from  40  to  60  per  cent  of  the  compounds  show 
enough  antlered  characteristics  to  be  separable  from  vestigial,  and  they 
approach  still  closer  in  type  to  the  pure  antlered  (fig.  77,  h). 


■%■:! 


OF   MUTANT   CHARACTERS. 


215 


Text-figure  78. — Strap-antlered  compounds.     Fig.  786,  showing  the  dominance  of  antlcred.  is 
of  a  male,  and  78a  the  less  extreme  corresponding  female. 


216  THE    SECOND-CHROMOSOME    GROUP 

A  similar  study  has  been  made  by  Morgan  of  the  compounds  between 
strap  and  antlered.  In  these  strap-antlered  compounds,  both  males 
and  females,  the  antlered  allelomorph  dominates  the  strap,  so  that  the 
flies  are  in  the  mass  scarcely  to  be  distinguished  from  antlered  (fig.  78,  a 
and  78,  6). 

DACHS  id). 

(Plate  10,  figures  \a  to  Id.) 

ORIGIN   OF  DACHS. 

The  mutant  now  called  dachs  had  a  double  origin.  Morgan  found 
in  certain  experiments  that  the  venation  of  the  wing  of  many  of  the 
flies  was  aberrant  (October  1912).  This  mutant,  which  he  called 
"shifty,"  was  characterized  by  a  reduction  and  shifting  of  the  veins  in 
the  basal  region  of  the  wing.  Often  the  second  longitudinal  vein  is 
joined  to  the  third  near  its  base  or  even  distal  to  the  anterior  cross- vein 
(plate  10,  figs.  \h,\c,ld).  This  anterior  cross- vein  is  itself  often  absent 
(figs.  1  band  1  c),  while  in  other  cases  there  is  an  extra  cross- vein  between 
the  second  and  third  longitudinal  veins  and  placed  nearer  the  base  of 
the  wing  than  the  anterior  cross-vein  (fig.  1  h) .  The  wing  as  a  whole 
is  slightly  shorter  than  normal  and  occasionally  is  much  more  reduced, 
with  an  accompanying  reduction  of  the  venation. 

Shortly  after  this  (November  22,  1912)  Bridges  found  in  the  F2  of  a 
cross  of  sable  male  to  wild  female  6  females  with  short  legs  among 
about  400  offspring  (C146).  The  F2  was  from  a  mass-culture,  so  that 
there  is  no  significance  in  finding  more  than  one  and  less  than  a  quarter 
of  the  flies  with  this  character.  The  fact  that  all  these  flies  were 
females  also  was  of  no  significance,  except  as  an  indication  that  the 
character  was  probably  autosomal.  A  pure  stock  of  "dachs,"  as  the 
mutation  was  called,  was  soon  extracted  from  the  ofTspring  of  the  dachs 
females  mated  to  their  wild-type  brothers.  Some  further  selection 
was  necessary  to  eliminate  sable  from  the  stock. 

DESCRIPTION  OF  DACHS. 

The  characteristic  feature  of  dachs  is  the  fact  that  the  tarsus  of  each 
leg  has  only  4  joints  instead  of  the  5  possessed  by  nearly  all  other  Diptera 
(plate  10,  fig.  1  a).  These  joints  are  themselves  perfectly  distinct  and 
normal,  except  for  being  slightly  shortened.  The  proximal  one  has, 
in  the  male,  the  sex-comb  typical  of  the  proximal  joint  of  the  normal 
male,  so  that  the  omitted  joint  is  one  of  the  more  distal  ones — perhaps 
the  penultimate.  The  rest  of  the  leg,  especially  the  tibia,  is  also 
shortened.  The  legs  are  drawn  in  close,  so  that  they  seem  much 
shorter  than  they  are,  and  the  "dachs"  appearance  is  accentuated. 
It  was  soon  noticed  that  the  venation  was  aberrant  in  the  same  manner 
as  in  "shifty' '  flies,  and  an  examination  of  the  shifty  stock  showed  that 
all  of  them  had  four-jointed  tarsi.  In  fact,  the  two  stocks  were  prob- 
ably identical.     Whether  they  were  of  single  origin  (from  the  wild 


li 


PLATE  10 


mi 


OF    MUTANT    CHARACTERS. 


217 


stock?)  or  whether  there  were  two  independent  mutations  is  uncertain. 
Both  occurrences  have  contributed  to  similar  "epidemics  of  mutation' ' 
in  the  cases  of  purple,  jaunty,  arc,  etc. 

CHROMOSOME  CARRYING  DACHS. 

Since  it  had  become  apparent  while  pure  stock  was  being  extracted 
that  dachs  was  recessive  and  not  sex-linked,  we  proceeded  directlj'  to 
tests  of  its  autosome  group.  A  dachs  male  was  out-crossed  to  a  black 
female,  and  from  a  pair  of  the  wild-type  Fi  flies  an  F2  culture  was 
raised  (table  60) . 

Table  60. — Pi,  dachs  cf  X  black  9  ■  Fi  wild-type  cf  X  /^i  wild-type  9 . 


Jan.  7.  1913. 

Wild-type. 

Dachs. 

Black. 

Dachs  black. 

II  4 

186 

71 

93 

0 

The  F2  flies  were  in  the  2:1:1:0  ratio,  which  had  become  recog- 
nized as  the  typical  result  for  two  recessives  in  the  same  autosome 
crossed  to  each  other  and  carried  to  F2  ("repulsion"  F2).  This  ratio 
is  the  necessary  result  of  the  absence  of  crossing-over  in  the  male  and 
is  independent  of  the  amount  of  crossing-over  in  the  female. 

A  similar  cross  of  dachs  by  curved  likewise  gave  no  double  recessives 
in  F2  (table  61).  The  reason  in  this  case  for  crossing  to  two  different 
recessives  in  the  same  chromosome  was  to  locate  dachs  more  speedily 

Table  61.— Pi,  dachs   9  9    X  curved  cfd^.    Pi  wild-type   9  9    +  Pi 

wild-type  cf  cf. 


Jan.  6,  1913. 

Wild-type. 

Dachs. 

Curved. 

Dachs  curved. 

II  8 

512 

166 
204 

169 
47 
41 

245 
89 
96 

0 
0 
0 

II  10 

II  13 

Total 

882 

257 

430 

0 

by  working  out  simultaneously  two  cross-over  values.  However,  the 
dachs  curved  cross  was  not  carried  to  the  back-cross  stage,  because 
at  that  time  the  locus  of  curved  was  itself  not  sufficiently  well  estab- 
lished and  secondarily  because  dachs  seemed  poorly  viable  in  the 
dachs  curved  F3. 

From  the  dachs  X  black  F2,  dachs  and  blacks  were  crossed  en  7nasse, 
and  in  F3,  a  few  dachs  black  double  recessive  were  secured.  One  of 
these  was  crossed  to  a  wild  male  as  the  Pi  for  the  j^roposed  crosses, 
and  the  rest  were  mated  together  to  supply  a  dachs  black  stock  to  be 
used  in  the  back-cross  tests. 


218 


THE    SECOND-CHROMOSOME    GROUP 


Three  F2  mass-cultures  were  raised  (table  62),  from  which  a  rough 
calculation  of  the  amount  of  crossing-over  was  made,  as  follows:  The 
class  dachs  black  is  a  non-cross-over  simple  class.  Each  of  the  two 
complementary  classes  dachs  and  black  is  a  cross-over  class.  The  wild- 
type  class  is  composite,  including  the  wild-type  non-cross-over  class 
complementary  to  the  dachs  black  class,  and  also  all  the  flies  coming 


Table  62.- 

—Pi,  dachs 

)lack    9    X  wild 

cf. 

Fi  wild-type  9  9    +   Fi  wild-type  cf  cf . 

March  18.  1913. 

Dachs  black. 

Wild-tj^pe. 

Dachs. 

Black. 

II  34 

113 

58 
85 

403 
263 
339 

34 
25 

28 

32 
20 
24 

II  35 

II  36 

Total 

256 

1,005 

87 

76 

B.  C,  Fi  wild-type  c?  X  dachs  black  9  from  stock. 

April  1,  1913. 

Dachs  black. 

Wild-type. 

Dachs. 

Black. 

II  37 

72 

98 

0 

0 

B.  C.  Fi  wild-type  9   X  dachs  black  cT  from  stock. 

June  30,  1913. 

Dachs  black. 

Wild-type. 

Dachs. 

Black. 

II  40 

64 

47 
52 
13 
14 

27 
58 

91 
112 
75 
53 
56 
38 
70 

9 
6 
9 
3 
4 
9 
15 

12 
25 
15 
9 
9 
16 
22 

II  56 

II  57 

II  91 

II  94 

II  98 

II98r 

Total 

275 

495 

55 

108 

& 


from  that  half  of  the  sperm  which  carried  the  wild-type  chromosome, 
for  which  reason  it  can  not  be  used  in  a  simple  calculation.  The  aver- 
age of  the  dachs  and  the  black  classes  (  — — —  =  82  ]  was  used  as  the 

cross-over  class  to  compare  with  the  256  dachs  black  non-cross-overs. 
The  percentage  of  crossing-over  thus  calculated  was  24.3,  and  this  was 
temporarily  taken  to  be  the  dachs  black  distance.  The  position  of 
dachs  was  assumed  to  be  to  the  right  of  black,  since  all  the  other 
mutants  thus  far  found  were  in  that  direction. 

A  male  test  was  made  by  back-crossing  an  Fi  male  by  a  dachs  black 
female  (table  62).    There  were  no  cross-overs  in  a  total  of  170  flies. 


OF   MUTANT   CHARACTERS. 


219 


The  back-cross  tests  of  the  female  (table  62),  somewhat  delayed, 
gave  a  total  of  933  flies,  of  which  103  were  cross-overs.  The  percentaj^e 
of  crossing-over  calculated  from  these  back-cross  results  was  17.7 — 
a  much  more  dependable  figure  than  that  derived  from  the  F2. 


Table  63. — Pi,  dachs  black  vestigial  cf  c?'  X  wild  9  9 . 

dachs  black  vestigial  cf  cf  from  stock. 


Fi  wild-type   9    X 


Dec.  10,  1913. 

d                h                Vg 

d     1 

d     b 

1 

d     1 

I    rg 

Total. 

b        Vg 

1           vg 

IM 

Dachs 

black 

vestigial. 

Wild- 
type. 

Dachs. 

Black 
vestigial. 

Dachs 
black. 

Vestigial. 

Dachs 
vestigial. 

Black. 

II  114 

99 
117 
95 
85 
75 
68 

116 
133 
100 
89 
67 
102 

25 
30 
16 
22 
11 
13 

19 
34 
14 

21 
16 

18 

23 
18 
19 
23 
9 
14 

20 
20 
15 
22 
12 
25 

5 
4 
4 

3 

1 
2 

2 
4 
4 
2 
1 
1 

309 
360 
267 
267 
192 
243 

II  115 

II  116 

II  117 

II  119 

II  138 

Total 

539 

607 

117 

122 

106 

114 

19 

14 

1,638 

One  more  experiment  was  needed  to  finish  the  determination  of  the 
locus  of  dachs.  The  locus  of  dachs  was  known  to  be  about  18  units 
from  that  of  black,  and  while  it  had  been  assumed  that  dachs  lies  to 
the  right  of  black,  this  could  only  be  established  by  finding  the  cross- 
over value  for  dachs  and  another  of  the  mutants  whose  locus  was  known. 
Vestigial  was  chosen  for  this  test  and  preparations  were  made  to  carry 
out  a  balanced  triple  back-cross.  The  triple-recessive  dachs  black  ves- 
tigia,l  was  obtained  in  F3  from  the  cross  of  dachs  black  to  black  vestigial. 


Table  64. — Pi,    dachs    cf  cf    X    black  vestigial    9  9.     Fi   wild-type 

dachs  black  vestigial  cf  cf'  from  stock. 


9     X 


Dec.  11,  1913. 

d 

d         \        h            Vg 

d          1 

'•ff 

d     1 

b   1 

Total. 

b             Vg 

i 

b     1 

1                1           Vg 

Dachs. 

Black 
vestigial. 

Dachs 

black 

vestigial. 

Wild- 
type. 

Dachs 
vestigial. 

Black. 

Dachs 
black. 

Vestigial. 

II  120 

88 
51 
81 
87 
93 
74 

135 

79 

98 

110 

147 

70 

12 
12 
10 
16 
20 
12 

29 
15 
36 
43 
30 
16 

22 
8 
7 
23 
15 
18 

26 
18 
21 
19 
27 
17 

3 

1 
3 
3 

1 
2 

3 

318 
1S4 
261 
306 
344 
209 

II  121 

II  122 

5 
5 
5 

II  123 

II  124 

II  126 

Total 

474 

639 

82 

175 

93 

128 

13 

18 

1,622 

The  triple  back-cross  was  made  to  the  extent  of  about  1,000  flies  in 
three  of  the  four  possible  ways  (tables  63,  64,  and  65)  and  gave  a  grand 
total  of  4,892  flies  (table  66)  of  which  3,329  were  non-cross-overs,  757 
were  cross-overs  between  dachs  and  black,  689  were  cross-overs 
between  black  and  vestigial,  and  117  were  double  cross-overs. 


220 


THE    SECOND-CHROMOSOME    GROUP 


As  soon  as  the  first  flies  from  the  triple  back-cross  had  begun  to  hatch 
it  became  evident  that  the  locus  of  dachs  is  to  the  left  of  black  and  not 
to  the  right.  The  discovery  that  streak,  a  dominant,  was  so  far  to  the 
left  of  black  that  it  gave  very  free  crossing-over  had  just  been  made 
and  had  led  to  the  most  extensive  recasting  that  any  of  our  maps  had 
been  subjected  to.  The  location  of  dachs  in  the  middle  of  this  long 
gap  was  therefore  very  welcome. 

Table  65. — Pi,  dachs  black  cf  cf   X  vestigial   9  9.     Fi  wild  type   9   dachs 

black-vestigial  cf  cf  from  stock. 


Dec.  11,  1913. 

d         b 

Vg 

d           1                  Vg 

1      b 

d        b           \       Vg 

d     1          1 

\      b         \vg 

Total. 

Dachs 
black. 

Vestigial. 

Dachs 
vestigial. 

Black. 

Dachs 

black 

vestigial. 

Wild- 
type. 

Dachs. 

Black 
vestigial. 

II  127 

69 
111 

78 
101 
109 

96 
109 

82 
141 
174 

28 
23 
13 
30 
26 

29 
20 
19 
34 
39 

26 
32 
10 

18 
27 

24 
31 
16 
31 
33 

3 

4 

3 

4 

12 

5 
6 
2 

8 
6 

280 
336 
223 
367 
426 

II  128 

II  129 

II  l.so 

II  131 

Total 

468 

602 

120 

141 

113 

135 

26 

27 

1,632 

The  total  amount  of  crossing-over  between  dachs  and  black  as  calcu- 
lated from  this  balanced  experiment  was  17.9  units,  which  agreed  with 
the  17.7  units  found  in  the  simple  dachs  black  back-cross. 

Table  66. — Linkage  of  dachs  black  and  vestigial  with  balanced  inviability. 


Dec.  10,  1913. 

1 

1 

— 1 — 1 — 

Total. 

Cross 

-over  values. 

db 

b   Vg 

d  Vg 

d  b  Vg 

d 

1,146 
1,113 
1,070 

239 
257 
261 

220 
221 

248 

33 
31 
53 

1,638 
1,622 
1,632 

16.6 

17.8 
19.2 

15.5 
15.5 

18.4 

28.1 
29.5 
31.2 

b        Vg 

d      b 

Vg 

Total 

3 ,  329 

757 

689 

117 

4,892 

17.9 

16.5 

29.7 

Table  67  gives  the  summary  of  the  crossing-over  data  including 
dachs.  The  calculation  of  the  locus  of  dachs  on  the  basis  of  all  the 
data  is  17.5  units  to  the  left  of  black,  or  referred  to  star  as  the  zero- 
point  at  29.0. 

VALUATION  OF   DACHS. 

The  usefulness  of  dachs  is  limited  only  by  its  rather  poor  and  erratic 
viability.  In  many  experiments  the  viability  of  dachs  is  up  to  par,  but 
in  combination  with  certain  other  characters  it  has  been  unsatisfactory; 
thus  the  stock  called  "tt"  (dbp^cp^Sp)  is  poorly  viable  and  almost 
useless,  while  the  ''tt  — "  stock,  which  differs  only  in  the  omission  of 


OF   MUTANT   CHARACTERS. 


221 


Table.  67.- 

—Summary  of  the  cross-over  data  involving  dachs. 

Loci. 

Total. 

Cross- 
overs. 

Per 

cent. 

Date. 

By- 

Reference. 

Star  dachs .... 

96 

31 

32.3 

Sept.  12,  1915 

Bridges 

^       .S'           Fj,  tlath.-i  flies; 
'•          d           2141   2210. 

152 

53 

34.8 

Sept.  12,  1915 

Do. 

Idem,  notniachs  flics. 

1,617 

425 

26.3 

Sept.  15,  1915 

Do. 

S' 
S';  2  B.C.;  2146-2305. 

369 

112 

30.4 

Oct.     6,  1915 

Do. 

S' 
di;   —^  F,;  2217-2659. 

211 

57 

27.1 

Nov.  18. 1915 

Do. 

di:—2      B.C.;  2460. 

Streak  dachs . . 

1,027 

271 

26.4 

Aug.  24,  1916 
May—,  1914 

Do. 
Muller 

„,    '^'              /"r  B.C.:  4999- 
Std          5110. 

.\m.  Nat..  1916,  p.  422. 

3,472 

949 

27.3 

462 

45 

9,7 

Dachs  black. .  . 
Dachs  purple . . 

396 

64 

16.2 

Aug.  24.  1916 

Mar.  18. 1913 
June  30,  1913 
Dec.  10,  1913 

May  — ,  1914 
May  — ,  1914 

Bridges 

Bridges 
Do. 
Do. 

Muller 
Muller 

^.    "S'            PrB.  C:  499ft- 
'^'        Std           5110. 

d;d  6.  Fj;  II  34-11  36. 
d;  db  B.  C:  II  40-11  98r. 
d;  d  h  Tg  balanced  B.  C; 

II  114-11  1.38. 
Am.  Nat.,  1916,  p.  422. 

Am.  Nat..  1916,  p.  422. 

858 

109 

12.7 

338 

933 

4,892 

462 

82 
163 

874 

77 

24.3 

17.5 
17.9 

16.7 

6,725 

1,196 

17.8 

462 

97 

21.0 

Dachs  vestigial. 

Dachs  curved  . 
Dachs  speck. .  . 
Dachs  balloon. 

1,027 

196 

19.1 

Aug.  24,  1916 

Dec.  20,  1913 
May  —  1914 

May  — ,  1914 
May  — ,  1914 
May—,  1914 

Bridges 

Bridges 
Muller 

Muller 
Do. 
Do. 

„.  S'            Pr  B.C.;4999- 
'^'         Std             5110. 

d;  d  b  Tg  balanced  B.  C; 

II  114-11  138. 
Am.  Nat..  1916.  p.  422. 

Do. 
Do. 
Do. 

1,489 

293 

19.7 

4,892 
462 

1,456 
129 

29.7 
27.9 

5,354 

1,585 

29.6 

462 
462 
462 

145 
231 
231 

31.4 
50.0 
50.0 

dachs,  is  entirely  normal  in  viability.  In  all  other  respects  dachs  is  of 
first  rank.  Since  the  character  used  in  classification  is  the  number  of 
joints  of  the  tarsus,  there  is  no  masking  effect  possible  with  any  of  the 
other  second-chromosome  mutants.  The  recessiveness  of  dachs  is  com- 
plete, its  identification  is  perfect,  and  the  separations  are  easy  and  rapid. 
The  locus  of  dachs  is  such  that  it  is  the  most  important  connect  inp- 
link  between  the  left  end  of  the  chromosome  and  the  securely  cstab- 
hshed  and  well-mapped  region  from  bkck  to  the  right  end  of  the 
chromosome. 


222  THE    SECOND-CHROMOSOME    GROUP 

STREAK   (5,). 

(Plate  5,  figure  5,  and  Plate  10,  figure  2.) 
ORIGIN  OF   STREAK. 

In  a  stock  culture  from  a  pair  of  flies  with  the  mutant  called  'Top- 
wing"  (culture  C  149,  November  27,  1912),  Bridges  found  a  single 
female  which  had  a  prominent  broad,  dark  streak  down  the  middle  of 
the  thorax. 

STOCK  OF  STREAK. 

This  female  (non-virgin)  was  mated  to  several  of  her  brothers  and 
produced  many  streaks  among  the  offspring.  It  was  assumed  that 
the  character  was  recessive  and  that  some  of  the  brothers  had  been 
heterozygous.  No  Fi  counts  were  made  and  not  much  attention  was 
paid  to  the  character. 

Several  of  the  streak  individuals  were  mated  together  to  provide 
stock.  In  this  F2  culture  somewhat  more  than  half  (no  counts)  of  the 
offspring  were  streak  where  all  had  been  expected  to  be  streak.  This 
was  thought  to  indicate  a  ''poor"  character,  which,  like  truncate,  club 
(wings),  and  others,  shows  in  a  variable  proportion  of  the  flies  of  the 
same  genetic  constitution.  The  stock  was  carried  on  in  this  way  for 
two  more  generations,  when  it  was  decided  to  throw  it  away  as  being 
too  poor  to  repay  further  labor.  This  would  have  been  done  had  not 
Morgan  seen  in  this  character  a  bearing  on  a  selection  problem  which 
he  had  been  carrying  out  for  over  two  years  on  the  thorax  pattern 
of  "with"  flies.  In  the  course  of  selections  for  a  still  darker  pattern 
three  notable  successes  had  been  obtained,  all  of  which  turned  out  to 
be  simply  new  mutations  (speck,  oUve,  and  band)  which  had  occurred 
in  the  selected  stocks,  but  which  gave  no  further  variability  or  progress 
when  once  the  stocks  were  pure  for  them.  In  streak  there  was  an 
example  of  a  dark  thorax  character  which  closely  resembled  in  pattern 
the  darkest  of  the  long  selected  "bands,"  though  not  as  dense  in  pig- 
mentation, but  which  had  arisen  entirely  independent  of  any  selection 
whatsoever. 

Later  the  trident  mutant  "trefoil"  (plate  5,  fig.  6)  likewise  arose 
independent  of  selection.  These  independent  mutations  and  the  fact 
that  during  this  same  period  over  a  hundred  other  mutations  affecting 
every  part  of  the  body  had  appeared  in  Drosophila,  left  no  basis  what- 
ever for  the  supposition  that  the  selection  had  had  any  effect  what- 
ever on  either  the  frequency  or  the  nature  of  the  mutations,  or  that  any 
other  process,  aside  from  the  production  of  three  definite  mutations, 
had  contributed  to  the  success  of  the  selection. 

Morgan  selected  the  streak  stock  for  about  six  months,  though  not 
very  vigorously,  without  increasing  the  intensity  of  the  pattern  or  the 
frequency  of  the  streak  individuals. 


OF    MUTANT    CHARACTERS. 


223 


DESCRIPTION  OF  STREAK. 

The  principal  characteristic  of  streak  flies  is  the  hand  of  pifjmont 
along  the  thorax  and  scutellum.  This  band  seems  to  he  rather  deep- 
lying,  and  is  possibly  situated  in  a  different  layer  from  that  in  which 
the  other  pigment  characters  develop.  There  is  considerable  variation 
in  both  the  intensity  and  the  extent  of  the  dark  color.  In  its  greatest 
development  it  is  a  solid  band,  like  that  of  colored  figure  5,  filling  in 
the  entire  region  between  the  dorso-central  bristles  and  extending  over 
the  entire  scutellum.  In  less-developed  types  the  weakening  starts  in 
the  region  ahead  of  the  dorso-central  bristles  and  is  most  pronounced 
between  the  prongs  of  the  trident  pattern,  so  that  an  appearance  much 
like  typical  band  is  given.  (For  figures  of  "with,"  band,  and  trefoil, 
see  Alechanism  of  Mendelian  Heredity,  p.  206). 

The  intensity  of  color  is  never  very  great  and  the  color  may  nearly 
vanish.  However,  there  are  other  accessory  characteristics  that  aid 
in  the  classification.  Chief  of  these  is  a  flattening  of  the  thorax  and 
the  appearance  of  bubbles.  Both  of  these  effects  seem  to  be  due  to  an 
ill  development  of  the  underlying  muscles.  There  appear  to  be  present 
in  the  thorax  large  spaces  or  sinuses  filled  only  with  blood  and  large 
bubbles.  Where  there  are  no  bubbles  present  this  condition  is  not  so 
easy  to  distinguish,  though  it  may  sometimes  be  made  out  by  slightly 
pressing  the  thorax.  The  wings  are  apt  to  droop  and  to  diverge 
slightly,  probably  also  on  account  of  the  muscular  condition. 

DOMINANCE  AND  LETHAL  EFFECT  OF  STREAK.  PARALLEL  TO 

YELLOW  MOUSE. 

The  occurrence  of  the  mutation  as  a  single  individual — a  female — 
in  a  pair  culture,  its  immediate  reappearance  in  about  half  the  Fi  flies 
after  crossing  to  normal  males,  and  the  failure  of  these  Fi  flies  to  breed 

Table  68. — Pi,  streak   9    X  wild  cT. 


July  22.  1914. 

Streak 
9. 

Streak 

Wild- 
type  9. 

Wild- 
type  cf. 

336         

23 
53 
37 
76 

22 
69 
37 

68 

25 
69 
48 
64 

28 
64 
43 
60 

391                 

393 

394 

Total 

189 

196 

206 

195 

true,  found  an  explanation  (rather  delayed)  in  the  assumption  that 
streak  was  an  autosomal  dominant.  Moreover,  the  fact  that  the 
stock  could  not  be  made  to  breed  true  (continually  producing  at  least 
a  third  of  the  offspring  wild-type)  and  that  repeated  pair  mat ings  as 
well  gave  this  same  result,  led  to  the  assumption  tliat  homozygous 
individuals  were  not  produced.     This  case  was  seen  to  be  a  parallel  to 


224 


THE    SECOND-CHROMOSOME    GROUP 


the  well-known  case  of  the  yellow  mouse,  and  was  the  first  of  many 
to  be  found  in  Drosophila,  where  a  homozygous  dominant  is  lethal. 

Outerosses  of  streak  by  w^ld  gave  in  Fi  streaks  as  approximately 
half  of  the  flies.  The  records  of  these  early  out-crosses  were  lost  (note- 
book S  II),  but  similar  out-crosses  made  later  illustrate  the  fact  as  well 
(table  68). 

CHROMOSOME  CARRYING  STREAK. 

The  next  task  was  to  determine  in  which  chromosome  the  gene  for 
streak  is  located.  This  was  done  by  back-cross  tests  of  the  male  for 
black  (II  chromosome)  and  pink  (III  chromosome). 

Table  69. — Pi,  streak  9   X  pink  cf;  Fi  streak  cf  X  pink  9  of  stock. 


July  7,  1913. 

Streak. 

Pink. 

streak 
pink. 

Wild- 
type. 

D  7 

90 
65 

133 
50 

71 

77 

117 
64 

D  7r 

Total 

155 

183 

148 

181 

Streak  males  heterozygous  for  pink  were  produced  from  the  mating 
of  streak  female  by  pink  male.  Two  of  these  Fi  males  were  back-crossed 
to  pink  females  and  produced  a  total  of  667  offspring,  329  of  which 
were  recombinations  (table  69) .  The  presence  of  the  streak-pink  and 
the  wild-type  flies  as  49.3  per  cent  of  the  whole  proved  that  streak  was 
not  in  the  third  chromosome,  since  independent  assortment  was  demon- 
strated. 

Table  70. — Pi,  streak   9    X  black  cf ;  Fi  streak  cf   X  black   9  of  stock. 


July  7,  1913. 

Streak. 

Black. 

Streak 
black. 

Wild- 
type. 

D  5 

19 

21 

0 

0 

In  the  back-cross  test  of  the  streak  male  heterozygous  for  black  no 
recombination  occurred.  Every  one  of  the  19  not-black  flies  was 
distinctly  streak,  and  likewise  none  of  the  21  black  flies  showed  a  trace 
of  streak  (table  70).  This  result  was  due  to  the  fact  that  the  locus  of 
streak  is  in  the  second  chromosome  and  the  lack  of  crossing-over  in 
the  male. 

LOCUS  OF  STREAK. 

Immediately  following  the  appearance  of  the  first  flies  in  the  pre- 
ceding back-cross  tests  of  the  male,  a  test  of  the  locus  of  streak  was 
made  by  means  of  the  mutant  morula,  which  had  itself  just  been 
mapped  at  the  right  end  of  the  second  chromosome. 

Back-cross  tests  of  Fi  streak  females,  from  the  cross  of  streak  females 
by  morula  males,  gave  a  total  of  876  flies,  of  which  405  or  46.2  per  cent 
were  cross-overs  (table  71). 


OF    MUTANT    CHARACTERS. 


225 


This  very  free  crossing-over  between  streak  and  morula  indicated 
that  streak  was  far  away  from  the  right  end  of  the  chromosome,  where 
the  gene  for  morula  had  been  located.  It  was  thought  thiit  the  locus 
of  streak  was  in  the  neighborhood  of  bhick  (which  was  at  that  time 
considered  the  left  end  of  the  chromosome)  or  purple,  which  was  not 
far  from  black.  It  did  not  seem  probable  that  an  accurate  classifi- 
cation of  streak  and  black  could  be  made  at  the  same  time,  so  purple 
was  used  instead. 

Table  71. — Pi,  streak   9    X  morula  cf;  Fi  streak   9    X  morula  cf  of  stock. 


Aug.  24.  1913. 

Streak. 

Morula. 

Streak- 
niorula. 

Wild- 
type. 

II  64    

11 

.50 

.5.5 

124 

S 

47 

55 

121 

4 

40 

44 

130 

6 
31 
Gl 
89 

II  82 

II  92 

II  97 

Total 

240 

231 

218 

187 

A  three-locus  experiment  partly  balanced  for  inviability  was  carried 
out.  A  streak  female  was  out-crossed  to  a  purple  curved  male  and  Fi 
streak  females  were  back-crossed  by  purple  curved  males.  Since 
streak  is  a  dominant,  the  triple  recessive  not-streak  purple  curved  was  a 
double  mutant  form,  which  was  a  great  saving  of  labor  over  the  ordinary 
case,  in  which  the  triple  mutant  multiple  recessive  has  to  be  made  up. 

Table  72. — Pi,  streak   9    X  purple  curved  cf ;  B.C.,  Fi  streak   9    X  purple 

curved  d^  of  stock. 


Nov.  6,  1913. 

St 

St       1 

Pr      c 

St 

1    c 

St      1      Pr     1 

Pr           C 

1 

Pr         1 

1              1    c 

Streak. 

Pvu-ple 
curved. 

Streak 
purple 
curved. 

Wild- 
type. 

Streak 
curved. 

Purple. 

Streak 
purple. 

Cuned. 

II  103 

82 
83 
46 

81 
91 
52 

45 
57 
18 

49 
55 
23 

31 
27 
14 

28 

18 

9 

9 
14 

8 

12 
19 

7 

II  104 

II  110 

Total 

211 

224 

120 

127 

72 

53 

31 

38 

The  result  of  the  back-cross  (table  72)  was  surprising,  since  it  upset 
the  ill-founded  notion  that  black  was  at  the  left  end  of  the  second 
chromosome.  The  cross-over  values  (streak  purple  =  36.0,  jnirple 
curv'ed  24.5,  streak  curved  45.7)  and  the  double  cross-over  classes 
(streak  purple  versus  curved)  showed  that  streak  was  fully  40  units  to 
the  left  of  purple  (allowing  for  double  crossing-over).  No  trouble  in 
classifying  streak  was  met  in  this  experiment,  so  that  all  of  the  flies  are 
available  for  the  calculation. 

From  the  streak  purple  and  the  curved  flies  that  appeared  in  the 
back-cross  just  described  a  Pi  mating  was  made  for  the  second  type  of 


226 


THE    SECOND-CHROMOSOME    GROUP 


back-cross  (table  73).  This  second  back-cross  gave  linkage  results 
which  differed  only  very  slightly  from  those  of  the  first,  and  in  such  a 
way  that  by  combining  the  two  sets  of  data  the  deviations  of  one  tend 
to  balance  those  of  the  other  and  more  nearly  correct  values  can  be 
calculated. 


Table  73. — Pi,  streak  purple  9    X  curved  cf ;  B.C.,  Fi  streak  9    X 

curved  cf  of  stock. 


purple 


Dec.  18,  1913. 

St            Pr 

St         1     c 

St       Pr        \     C 

St    1 

I 

c 

1  Pr 

1 

\     Pr      \     C 

streak 
purple. 

Curved. 

Streak 
curved. 

Purple. 

Streak 
purple 
curved. 

Wild- 
type. 

Streak. 

Purple 
curved. 

II  1.36 

66 
29 
26 
24 
54 
24 
23 

58 
27 
27 
45 
53 
16 
24 

23 
12 
8 
25 
22 
14 
13 

33 
16 
12 
29 
32 
8 
7 

10 
3 
5 
9 

12 
6 
5 

11 

7 
10 
14 
14 

2 

9 

7 
7 
2 
5 
8 
1 
2 

5 
2 

4 
5 
8 
3 
3 

II  137 

13 

15 

16 

23 

24 

Total 

246 

250 

117 

137 

50 

67 

32 

30 

=  99.8 


) 


The  combined  data  gave  1,807  individuals,  of  which  931  were  non- 
cross-overs,  501  cross-overs  between  streak  and  purple,  244  cross-overs 
between  purple  and  curved,  and  131  double  cross-overs.  The  cross- 
over values  calculated  from  this  distribution  are  streak  purple  35.0 
per  cent,  purple  curved  20.7  per  cent,  and  streak  curved,  41.2  per  cent. 

The  coincidence  from  the  first  back-cross  was  98.0  and  from  the 
second  102.0.     The  coincidence  from  the  combined  data  was  99.8 

/1807X 131X100 

V       632X375 

For  a  section  of  this  great  length  and  involving  this  particular  region 
the  net  result  was  that  the  occurrence  of  a  cross-over  in  one  section  was 
without  effect  upon  the  occurrence  of  a  cross-over  in  the  other  section. 
The  locus  of  streak  as  calculated  from  the  above  data,  making 
allowance  for  the  probable  amount  of  double  crossing-over,  was  40.6 
to  the  left  of  purple  or  34.7  units  to  the  left  of  black,  which  was  the 
locus  farthest  to  the  left  of  those  previously  determined.  This  great 
gap  was  almost  immediately  filled  by  the  mapping  of  dachs  at  17.9 
units  to  the  left  of  black,  or  almost  exactly  midway  between  the  two. 
This  position  of  dachs  offered  a  new  base  of  reference  for  streak  and 
one  much  more  dependable  than  the  remote  purple.  The  data  on 
which  a  direct  determination  of  the  streak  dachs  distance  was  made  is 
included  in  the  section  on  star,  for  by  means  of  a  quadruple  back-cross 
involving  star,  streak,  dachs,  and  purple  the  loci  of  both  star  and  streak 
were  linked  up  with  the  portions  already  mapped.  The  streak  | 
dachs  interval  was  found  by  this  experiment  to  be  about  16.2  units. 


OF   MUTANT    CHARACTERS. 


227 


The  calculation  of  the  locus  of  streak  on  the  basis  of  all  the  available 
data  places  it  at  13.6  units  to  the  left  of  darhs  and  15.4  units  to  the 
right  of  star,  star  being  the  zero-point  for  the  chromosome. 

A  summary  of  the  linkage  data  directly  involving  streak  is  given  in 
table  74. 

Table  74. — Summary  of  cross-over  data  involving  streak. 


Loci. 

Total. 

Cross- 
overs. 

Per 

cent. 

Date. 

By- 

Referencft. 

Star  streak 

396 

63 

15.9 

Aug.  24,  1916 

Bridges 

S'            Pr 
S';       ^^^     'B.C.:    S, 

flics  only;  4990  .''.110. 
Am.  Nat.,  1910.  p.  422. 

Streak  dachs .... 

462 

45 

9.7 

May  — ,  1914 

Mullcr 

Streak  black 

Streak  purple .... 

396 

64 

16.2 

Aug.  24,  1916 

May  — ,  1914 
Nov.    6.1913 
May  — ,  1914 

Bridges 

Muller 

Bridges 

Muller 

5':*^'             ^'H.C.Sk' 
Std 

flies  only;  4999-5110. 

Am.  Nat..  1916,  p.  422. 

St'  Si  Pr  c  balancofi  B. 

C;  II  103   II  124. 
Am.  Nat..  1910.  p.  422. 

858 

109 

12.7 

462 

120 

26.0 

1,807 
462 

632 
137 

35.0 
29.7 

396 

114 

28.8 

Aug.  24,  1916 

Bridges 

S';^'          ^^  B.C..  St 
iS't  d 

flie-s  only;  4999-5110. 

Am.  Nat..  1910.  p.  422. 

Sk'>   Sn      Pr  c    balanced 

B.C.;  II  10.V124. 
Am.  Nat..  1916,  p.  422. 

6,;  '*'*        B.C.;  69. 

Streak  vestigial . . 
Streak  curved .  .  . 

Streak  blistered. . 

2,665 

883 

33.1 

May  — ,  1914 
Nov.    6,1913 
May  — ,  1914 

Feb.  23,  1914 

Muller 

Bridges 

Muller 

Bridges 

462 

164 

35.5 

1,807 
462 

745 

178 

41.2 
38.5 

2,269 

923 

40.7 

11 

5 

45.0 

Streak  speck 

Streak  Vjalloon . . . 

462 
462 

242 
242 

52.3 
52.3 

May  — .  1914 
May  — ,  1914 

Mullcr 
Do. 

.\m.  Nat.,  1916.  p.  422. 
Do. 

Streak  morula.  . . 

876 

405 

46.3 

.\ug.  24,  1913 

Bridges 

Sf.    "''*              B.C.; 

TO, 

II  64-11  97. 

VALUATION  OF  STREAK. 

There  is  only  one  drawback — but  that  one  very  serious — to  the  use- 
fulness of  streak,  namely,  the  difficulty  of  separating  all  the  streaks 
from  the  wild-type.  In  most  of  the  experiments  conducted  by  l^ridges 
this  difficulty  was  not  great  enough  to  impair  the  accuracy  of  the  result. 
However,  a  streak  dachs  back-cross  was  attempted  and  abandoned, 

and  in  the  quadruple  back-cross  (  J^')  the  separation  is  not  com- 

\    Sf.  a    / 

plete  in  all  cultures.     In  these  cultures  the  first  separation  performed 

was  that  of  the  streak  from  the  not-streak,  without  regard  to  the  other 


228 


THE    SECOND-CHROMOSOME    GROUP 


character.  Among  the  streaks  the  other  mutant  characters  should 
be  distributed  in  the  same  ratio  as  among  all  the  flies,  so  that  tolerably 
accurate  calculations  could  be  made  using  streak  flies  only,  but  such  ex- 
periments are  ineflicient.  In  the  "progeny  test"  experiment  of  Muller 
this  difficulty  was  entirely  avoided,  since  the  easily  determined  presence 
or  the  absence  of  streak  from  a  progeny-test  culture  was  all  that  was 
required  to  classify  each  parent.  Streak  is  not  a  character  that  can 
be  successfully  handled  without  quite  extensive  experience,  and  even 
under  the  best  of  conditions  there  is  chance  of  error. 

In  favor  of  streak  is  its  location,  which  is  very  important  as  the 
link  between  star  and  the  rest  of  the  chromosomes.  A  favorable 
location  far  more  than  doubles  the  usefulness  of  a  character,  other 
things  being  equal.  In  viability  and  other  features  streak  is  satis- 
factory. 

COMMA. 

(Text-figure  79.) 

ORIGIN  OF  COMMA. 

In  one  of  the  F2  cultures  from  the  cross  of  dachs  by  pink,  there 
appeared  a  mutant  character  called  ''comma"  (culture  II  9,  February 
6, 1913),  which  consists  of  a  pair  of  chitinous 
thickenings  on  the  anterior  dorsal  part  of  the 
thorax  (fig.  79).  In  shape  these  thickenings 
are  like  a  pair  of  commas,  lying  back  to  back, 
with  the  blunt  tails  pointing  posteriorly,  and 
depressed  below  the  general  level  of  the 
surface.  This  character  was  confined  very 
largely  to  the  females,  of  which  about  20  per 
cent  showed  the  character;  a  few  of  the  males 
also  were  conomas. 

From  the  frequency  of  the  commas  it  was 
concluded  that  the  character  was  an  auto- 
somal recessive,  which  was  either  very  in- 
viable  or,  more  probably,  failed  to  show  in  all 
those  flies  which  were  homozygous.  In  either 
case  the  character  was  markedly  sex-limited  in  the  sense  that  under 
like  conditions  far  fewer  of  the  males  than  of  the  females  showed  the 

r»V)  o  T*o  p"!"  fiT* 

CHROMOSOME  CARRYING  COMMA. 

In  the  F2  of  the  dachs  pink  cross,  the  commas  seemed  to  be  distrib- 
uted at  random  among  the  pinks  and  the  wild-types,  while  none  were 
seen  among  the  dachs.  This  was  interpreted  as  meaning  that  the  locus 
is  in  the  second  chromosome.  To  test  this  point,  commas  were  out- 
crossed  to  pink  of  the  third  chromosome  and  to  vestigial  of  the  second 
chromosome  and  an  F2  mass-culture  was  raised  in  each  case  (tables 


Text-figure  79. — Diagram 
of  "comma." 


OF   MUTANT   CHARACTERS. 


229 


75  and  76).     Two  or  three  out-crosses  of  the  pink  comma  flies  were 
also  attempted  to  secure  Pi  for  a  back-cross,  but  these  failed. 

The  F2  of  the  comma  by  pink  gave  only  8  commas,  all  females,  among 
440  flies.  Of  these  8,  3  were  pink  commas,  so  that  comma  was  proved 
to  be  not  third-chromosome.  The  fewness  of  the  commas  was  partly 
due  to  the  crowding  of  the  mass-cultures,  but  more  to  the  fact  that  the 
character  fails  to  show  on  all  the  flies  that  are  genetically  commas. 

Table  75. — Pi,  comma  9  X  pink  cf.     Fi,  wild-type  9  9+  Fi  wild-type  cf  cf. 


Apr.  3,  1913. 

Wild-type. 

Comma. 

Pink. 

Comma  pink. 

9 

c? 

9 

d" 

9 

cf 

9 

d" 

M  24 

147 

163 

5 

55 

67 

3 

The  F2  from  the  cross  of  comma  by  vestigial  gave  18  females  and 
1  male  with  comma,  but  not  one  of  these  was  vestigial.  While  these 
numbers  are  not  large  enough  to  prove  that  comma  is  second-chromo- 
some, the  probablity  is  high  that  it  is. 

Table  76. — Pi,  comma  9    X  vestigial  cf.     Fi  wild-type  9  9   +  Fi 

wild-type  cf  cf. 


Apr.  3,  1913. 

Wild-type. 

Comma. 

Vestigial. 

Comma 
vestigial. 

9 

& 

9 

cT 

9 

d^ 

9 

c? 

M23 

282 

262 

18 

1 

68 

73 

0 

0 

Comma  reappeared  in  the  experiments  involving  "squat"  and 
followed  this  second-chromosome  mutant  in  distribution  in  such  a 
way  as  to  make  it  practically  certain  that  comma  is  also  in  the  second 
chromosome. 

VALUATION  OF  COMMA. 

Aside  from  carrying  on  a  stock  of  commas  for  a  few  generations  and 
noting  that  the  percentage  of  commas  was  seldom  above  30,  nothing 
further  was  done  with  this  mutant  because  of  the  poorness  of  the 
character.  When  present,  the  character  comma  was  perfectly  sharp 
and  clear,  even  when,  as  was  quite  often  the  case,  it  showed  on  only 
one  side  of  the  thorax. 

Perfectly  definite  and  trustworthy  classifications  can  be  made  with 
characters  such  as  these,  but  they  are  very  inefficient,  since  only  flies 
actually  showing  the  character  can  be  considered.  The  conclusions 
drawn  from  such  data  are  not  so  safe  as  the  classification,  since  it  has 
been  our  experience  that  such  characters  are  particularly  sensitive 
to  intensification  or  repression  (in  percentage  of  appearance)  by  the 
other  genes  present  in  the  crosses. 


230 


THE    SECOND-CHROMOSOME    GROUP 


MORULA  (m,). 

(Plate  10,  figures  3a  and  36.) 

ORIGIN  OF  MORULA. 

In  the  F2  from  the  cross  of  peach  (third-chromosome  recessive, 
allelomorph  of  pink)  by  wild,  two  red  males  were  found  that  had  only- 
very  inconspicuous  bristles  on  the  thorax  (M  20,  March  8,  1913). 

INHERITANCE  OF  MORULA. 

These  two  males  were  out-crossed  to  wild  females,  and  in  Fi  pro- 
duced only  wild-type  males  and  females.  Four  Fi  mass-cultures  were 
made  up,  and  in  F2  these  produced  (table  77)  a  total  of  1,950  flies,  of 
which  432  or  22.2  per  cent  were  ''spineless."  The  ''spineless"  flies 
were  exactly  as  numerous  among  the  F2  females  as  males,  from  which 
it  follows  that  the  character  is  an  autosomal  recessive  mutant.  There 
was  found  to  be  some  little  difficulty  in  classification,  and  it  is  certain 
that  a  few  of  the  genetically  spineless  individuals  were  included  among 
the  wild-type;  this  was  especially  true  in  culture  M  42. 

Table  77. — Pi,  '^ spineless'*  {morula)   d^cT    X  wild   9  9;  Fi  wild-type  cf  cf 

and  9  9  inbred  en  masse. 


Apr.  3,  1913. 

Wild- 
type  9. 

Wild- 
type  cf . 

"Spineless" 
9. 

"Spineless" 

M  31 

M31r 

M  42 

M43 

Total.... 

208 
164 
126 
264 

191 
176 
122 
262 

63 
44 
26 
83 

60 
43 
34 
79 

767 

751 

216 

216 

FEMALE  STERILITY  OF  MORULA. 

The  next  step  attempted  was  to  secure  a  pure  stock  of  "spineless" 
by  mating  together  en  masse  several  of  the  F2  individuals  from  M  31. 

It  was  discovered  that  this  stock  culture  was  not  showing  any  larvae, 
so  the  flies  were  put  in  a  fresh  bottle  and  several  other  "spineless" 
males  and  females  added.  This  culture  also  failed.  The  F2  cultures 
had  been  thrown  away  meanwhile,  so  that  it  was  not  possible  to  start 
other  stock  cultures.  The  flies  were  then  taken  from  the  mass-culture 
that  had  failed,  separated  as  to  sexes,  and  the  males  out-crossed  to 
wild  females  and  the  females  to  wild  males. 

The  out-cross  of  the  males  was  successful,  but  the  female  out-cross 
failed  entirely.  The  trouble,  then,  was  confined  to  the  females,  which 
so  far  as  tested  (about  15  females)  had  been  entirely  sterile  both  with 
similar  males  and  with  wild  males. 

The  "spineless"  females  that  hatched  in  the  F2  from  the  male  out- 
cross  were  tested  very  extensively.     Probably  as  many  as  150  such 


OF   MUTANT    CHARACTERS.  231 

females  were  tested  either  singly  or  in  mass-cultures,  and  no  offspring 
were  produced.  On  the  other  hand,  the  males  were  entirely  fertile. 
This  case  was  the  third  to  show  female  sterility.  Rudimentary 
females  usually  gave  no  offspring,  but  occasionally  gave  a  very  few 
which  were  found  to  be  almost  entirely  female.  An  extensive  series 
of  outcrosses  of  rudimentary  females  (carried  out  in  1912  by  Bridges) 
produced  a  total  of  623  females  and  only  9  males. 

The  sex-linked  character  "fused"  was  likewise  found  to  be  sterile 
as  to  its  females  and  fertile  as  to  its  males,  though  no  such  extensive 
tests  were  made  as  in  the  case  of  rudimentary  and  "spineless. "  Since 
these  three,  several  other  mutations  whose  females  were  completely 
sterile  and  three  mutations  with  completely  sterile  males  have  been 
found.  All  of  these  mutations  with  unisexual  sterility  have  been 
turned  over  to  Miss  Clara  J.  Lynch  for  further  investigation. 

After  the  failure  to  maintain  "spineless' '  stock  by  use  of  the  females, 
the  stock  was  run  by  mating  in  each  generation  "spineless"  males  by 
wild-type  sisters  heterozygous  for  the  gene. 

ARRANGEMENT  OF  THE  FACETS  OF  MORULA. 

At  this  time  it  was  noticed  that  there  was  present  in  the  "spineless " 
cultures  a  new  type  of  eye  modification,  which  was  called  "morula," 
since  in  it  the  facets  of  the  eye  had  lost  their  regular  pattern  and  were 
crowded  together  irregularly,  much  like  the  drupelets  of  a  mulberry. 
The  facets  tended  to  "round  up"  and  become  more  strongly  convex, 
and  to  become  more  circular  than  hexagonal  in  outline  (plate  10,  fig.  3  b). 
The  facets  were  also  irregular  in  size  and  color,  large  ones  being  usually 
darker  than  those  smaller.  The  eye  as  a  whole  was  somewhat  smaller 
than  normal  and  more  convex.  The  light  reflected  from  the  surface 
was  broken  up  into  many  twinkling  points  by  the  tiny  hairs  which  were 
found  to  be  pointing  in  all  directions  instead  of  only  radially  (figs.  3  b 
and  3  c).  This  feature  is  common  to  several  of  the  later  discovered 
moruloid  mutations  and  is  the  reason  for  the  name  "star"  borne  by 
the  most  useful  of  them  all. 

Most  of  the  morula  flies  were  found  to  be  also  "spineless;"  several 
counts  established  the  fact  that  every  "spineless"  was  at  the  same 
time  "morula, "  but  that  only  about  90  per  cent  of  the  " moruhis "  were 
"spineless."  This  fact  led  to  the  suspicion  that  the  two  characters 
were  effects  of  the  same  gene  and  that  while  the  "mom la"  was  a 
constant  index  of  the  mutation,  the  "  spineless "  might  be  called  an 
"accessory"  character.  This  agreed  with  the  difficulty  encountered 
previously  in  classifying  "spineless"  and  with  the  too  small  proportion 
separated  out.  The  differences  between  the  numbers  of  "morula" 
and  "spineless"  flies  gave  a  measure  of  the  unrehability  of  "spineless. " 
Throughout  subsequent  experiments  attention  was  paid  to  the  relation 
of  "spineless"  and  "morula,"  and  since  no  case  was  found  in  which  a 


232 


THE    SECOND-CHROMOSOME    GROUP 


"spineless"  was  not  also  "morula,"  the  conclusion  that  they  are 
effects  of  the  same  gene  is  justified.  The  name  "morula"  was  then 
retained,  and  the  name  "spineless"  was  given  to  the  third-chromosome 
recessive  which  now  bears  it. 

The  "spineless"  flies  must  have  had  the  "morula"  character  at  the 
time  of  their  discovery,  and  this  character  must  have  passed  unno- 
ticed for  several  generations,  during  which  several  hundred  such  flies 
were  examined.  That  such  a  conspicuous  character  should  be  present 
and  be  overlooked  would  be  almost  unbelievable  were  it  not  that  many 
other  similar  failures  have  been  made,  notably  in  the  cases  of  dachs 
(see  p.  216)  and  club.  In  the  case  of  club,  Morgan  found  and  worked 
with  the  wing-character  for  many  generations  without  discovering  the 
absence  of  the  pleural  bristles  which  is  the  constant  index  of  the  mutant, 
Bridges  surpassed  this  by  finding  in  another  stock  this  same  mutant, 
which  he  worked  with  as  a  bristle  character,  and  entirely  failed  to 
recognize  the  far  more  conspicuous  wing  modification  which  was  present. 

CHROMOSOME  CARRYING  MORULA. 

To  determine  whether  the  gene  for  "morula"  was  in  the  second 
chromosome,  a  morula  male  was  out-crossed  to  a  curved  female  and 
three  F2  pair  cultures  raised  (table  78) . 

Table  78. — Pi,  morula  cf   X  curved  9 ;  Fi  wild-type  9   -\-  Fx  wild-type  cf . 


June  28,  1913. 

Wild- 
type. 

Curved. 

Morula. 

Curved 
morula. 

M  48 

55 
56 
97 

22 
22 
42 

26 
24 
54 

0 
0 
0 

M  49 

M  50 

Total 

208 

86 

104 

0 

The  F2  ratio  was  plainly  a  2  : 1  :  1  :  0  ratio,  with  no  double  recessives, 
which  proved  that  morula  was  in  the  second  chromosome. 

An  attempt  to  obtain  the  curved  morula  double  recessive  from  F3 
or  F4  matings  failed,  but  in  F4  from  a  similar  cross  of  morula  to  black 
the  double  recessive  was  readily  obtained. 

LOCUS  OF  MORULA. 

From  this  difference  in  the  ease  of  obtaining  the  double  recessive  it 
was  suspected  that  morula  was  nearer  to  curved  than  to  black  in  the 
second  chromosome. 

It  became  apparent  in  F3  that  the  double  recessive  black  morula 
would  be  obtained  in  F4,  since  some  of  the  F2  black  females  and  morula 
males  mated  together  had  produced  in  F3  a  few  black  flies  which  were 
then  known  to  be  heterozygous  for  morula  and  which  must  produce 
black  morula  offspring  among  their  progeny  when  inbred.  Accord- 
ingly, by  making  an  Fi  mating  of  morula  male  by  black  female  at  the 


OF   MUTANT    CHARACTERS. 


233 


same  time  that  the  F3  blacks  were  inbred,  both  the  Fj  flies  and  the 
double  recessive  necessary  to  test  them  were  obtained  at  the  same 
time  and  a  generation  saved. 

Three  back-cross  cultures  were  raised  from  pairs  (table  79),  which 
gave  a  total  of  755  offspring,  of  which  353  or  4(3.8  per  cent  were  cross- 
overs. This  was  very  free  crossing-over,  comparable  with  the  black 
arc  and  black  balloon  values  previously  found. 


Table  79.- 


-Pi,  black   9  9    X  morula  cf^cf;  Fi  wild-type   9    X  black  morula 

cf  of  stock. 


Sept.  9,  1913. 

Non-cross-overa. 

Cross-overa. 

Black. 

Morula. 

Black 
morula. 

Wild- 
type. 

II  93 

66 
59 
73 

89 
49 
66 

73 
51 
59 

62 
55 
53 

II  95 

II  96 

Total .... 

198 

204 

183 

170 

Table  80. — Pi,  black  arc  9   X  morula  cf;  B.C.,  Fi  vnld-type   9    X  black  arc 

morula  cf  from  stock. 


Aug.    4,  1914. 

b         a 

h      1 

'»T 

b     a    1 

mr 

1  a 

1 

1       rnr 

Total. 

1       a 

Black 
arc. 

Morula. 

Black 
morula. 

Arc. 

Black 

arc 
morula. 

Wild- 
type. 

Black. 

Arc 
morula. 

364 

79 
62 

107 
77 
65 
74 

126 
71 
66 
45 

112 

78 
67 

101 
86 
69 
77 

105 
80 
73 
52 
63 

66 
61 
74 
57 
45 
47 
88 
65 
58 
31 
74 

65 
57 
93 
72 
59 
63 
81 
66 
52 
41 
64 

7 

5 

15 

12 

4 

7 

12 

3 

4 

3 

7 

9 
5 
7 

13 

10 
9 

10 
9 
6 
3 

14 

6 
2 
6 

5 
3 
5 
4 
3 
3 
3 

3 

1 
2 
5 
4 
4 
3 
2 
6 
1 
2 

313 
260 
405 
322 
261 
2H4 
430 
300 
268 
179 
339 

365 

366   

367 

368 

369 

383 

384 

385 

386 

387 

Total 

884 

Sol 

666 

713 

79 

95 

40 

33 

3,361 

From  a  comparison  of  these  values  and  from  the  fact  that  curved 
and  morula  had  not  crossed  over  readily,  it  was  concluded  that  the 
locus  of  morula  must  be  close  to  that  of  arc. 

An  effort  was  made  to  obtain  triple-recessive  black  arc  morula  ami 
black  balloon  morula.  This  latter  stock  was  not  obtained  at  all,  and 
the  former  was  secured  only  after  repeated  matings  of  (Fo,  F4,  and  Fe) 
black  arc  and  black  morula  flies. 

Triple  back-crosses  for  the  loci  black,  arc,  and  morula  were  made  in 
pairs  in  each  of  the  four  possible  ways  in  order  to  balance  the  invia- 
biUty  completely.     The  numbers  are  not  equal  in  the  ditlerent  experi- 


234 


THE    SECOND-CHROMOSOME    GROUP 


merits,  which  should  be  the  case  to  secure  the  most  perfect  balancing  of 
the  inviabiUty  (tables  80,  81,  82,  and  83). 

The  grand  totals  for  these  four  complementary  back-cross  experi- 
ments furnished  6,794  flies,  of  which  3,469  were  non-cross-overs,  2,791 
cross-overs  between  black  and  arc,  374  cross-overs  between  arc  and 

Table  81. — Pi,    black  arc  morula    cf    X  mild   9 ;  B.C.,  Fi  wild-type    9    X 

black  arc  morula  cf"  of  stock. 


Aug.  19,  1914. 

b          a 

nir 

b     1 

1 

a     mr 

b         Q 

1     inr 

b       1 
1  ^ 

1    rrir 
\ 

Total. 

Black 

arc 

morula. 

Wild- 
type. 

Black. 

Arc 
morula. 

Black 
arc. 

Morula. 

Black 
morula. 

Arc. 

443    

39 
89 
89 
28 
56 
36 
59 
49 
69 

66 
113 
85 
26 
45 
48 
81 
74 
75 

25 
107 
109 
22 
31 
22 
50 
28 
51 

41 
87 
56 
23 
49 
40 
72 
46 
53 

3 
7 
6 
1 
8 

12 
1 
4 

13 

9 

10 

11 

5 

9 

9 

11 

11 

7 

2 
1 
12 
1 
1 
3 
2 
4 
3 

2 
4 
11 
1 
3 
6 
2 
2 
7 

187 
418 
379 
107 
202 
176 
278 
218 
278 

444    

445    

453    

454 

465 

466 

467 

479 

Total 

514 

613 

445 

467 

55 

82 

29 

38 

2,243 

Table  82. — Pi,  black  morula  d*   X  arc   9 ;  B.C.,  Fi  wild-type   9    X    black 

arc  morula  cT  of  stock. 


Sept.  8,  1914. 

b 

mr 

b       1 

a 

b 
a 

1     f^r 

b     1  a 

mr 

Total. 

a 

1              »«r 

1       1 

Black 
morula. 

Arc. 

Black 
arc. 

Morula. 

Black. 

Arc 
morula. 

Black 

arc 
morula. 

Wild- 
type. 

477   

21 
37 

62 

26 
30 
57 

27 
34 
35 

27 
36 
44 

3 

1 
9 

2 
6 
6 

2 

2 

110 
144 
214 

510       

511 

1 

Total 

120 

113 

96 

107 

13 

14 

4 

3 

468 

Table  83. — Pi,  black   9    X  arc  monda  cf ;  B.C.,  F\  wild-type   9    X    black 

arc  morula  cf ,  from  stock. 


Sept.  27,  1914. 

b 

b      1     a     m-r 

b 

1      mr 

b     1     a 

1 

Total. 

a      mr 

1 

a      1 

i            1      r>,r 

Black. 

Arc 
morula. 

Black 

arc 
morula. 

Wild- 
type. 

Black 
morula. 

Arc. 

Black 
arc. 

Morula. 

571 

80 
51 
56 

69 
52 
66 

58 
40 
35 

61 

58 
45 

9 
2 
4 

8 
5 

8 

2 
4 

2 

2 
3 
2 

289 
215 
218 

572 

573 

Total 

187 

187 

133 

164 

15 

21 

8 

7       !     722 
1 

*. 


OF    MUTANT    CHARACTERS. 


235 


morula,  and  160  were  double  cross-overs  (table  84).  The  total  cross- 
overs between  arc  and  morula  were  534  or  7.9  per  cent.  The  black 
arc  cross-over  value  was  43.4  per  cent  and  the  black  morula  4(3. G  per 
cent,  which  agrees  with  the  46.8  per  cent  found  in  the  former  black 
morula  back-cross.  These  values  and  the  smallness  of  certain  cla.ssos 
thereby  known  to  be  double  cross-over  classes  established  the  position 
of  morula  to  the  right  of  arc,  and  7.9  units  distant. 

Table  84. — The  four  complemetitary  hack-cross  experiments  giving  data  on  the 

relations  of  black  arc,  atid  morula. 


Aug.  4,  1914. 

-1 

1 — 

Total. 

Cro8»-over   valuca. 

ba 

a  rrif 

b  nir 

b     a 

1,735 

1,127 

233 

374 

1,379 
912 
203 
297 

174 

137 
27 
36 

73 

67 

5 

15 

3,361 

2,243 

468 

722 

43.2 
43.6 
44.4 
43.2 

7.4 
9.1 
6.8 
7.1 

46.2 
46.7 
40.2 
4.61 

b     a     rriT 

b     mr 

a 

b 

a     nif 
Total 

3,469 

2,791 

374 

160 

6,794 

43.4 

7.9 

46.6 

The  coincidence  of  69.1  per  cent 


/160X6794X100 


')■ 


=  69.1)  is  rather 


2951X534 

low  for  distances  so  long  and  indicates  that  a  cross-over  between  arc 
and- morula  is  only  69  per  cent  as  likely  to  be  accompanied  by  a  cross- 
over between  black  and  arc,  as  would  be  the  case  if  the  two  regions 
were  independent. 

Table  85. — Summary  of  the  cross-over  data  involving  morula. 


Loci. 

Total. 

Cross- 
overs. 

Per 

cent. 

Date. 

By- 

Reference. 

Streak  morula. 
Black  morula. . 

Arc  morula 

876 

405 

46.3 

Aug.  24,  1913 

Sept.  28,  1913 
Aug.    4.1914 

Aug.    4,  1914 

Bridges 

Do. 

Do. 

Do. 

Sf,   **      B.C.;  II  64-11  97. 
nxr 

rtir;  ^      B.  C;  II  93-11  96. 
mr 

mr,  ba  mr  balanced  B.  C. ; 
364-573. 

mr',  ba  mr  balanced  B.  C; 
364-573. 

755 
6,794 

353 
3,165 

46.8 
46.6 

7,549 

3,518 

46.6 

6,794 

634 

7.9 

The  purple  arc  speck  back-cross  (table  54)  had  given  5.9  units  to 
the  right  of  speck.  Morula  is  therefore  situated  about  2  units  to  the 
right  of  speck.  A  summary  of  all  the  cross-over  data  including  m(iriila 
is  given  in  table  85,  from  which  the  locus  of  morula  is  calculated  as 
106.3  on  the  basis  of  star  as  the  zero-point. 


236  THE    SECOND-CHROMOSOME    GROUP 

VALUATION  OF  MORULA. 

The  locus  of  morula  is  the  farthest  to  the  right  of  the  workable 
mutants,  and  for  this  reason  is  valuable,  though  speck,  which  is  less 
than  2  units  to  the  left  of  morula,  will  probably  be  used  in  the  majority 
of  cases.  There  is  another  reason  for  the  preference  of  speck  over 
morula  in  general — that  morula  would  interfere  in  classification  with 
star,  which  is  the  most  useful  of  the  second-chromosome  mutants, 
while  speck  interferes  neither  with  star  nor  any  other  second-chromo- 
some mutant.  The  female  sterility  of  morula  also  limits  its  usefulness 
in  complex  experiments.  On  the  other  hand,  the  character  morula  is 
exceptionally  easy  and  certain  in  its  separability  from  the  wild-type, 
being  surpassed  in  this  regard  by  no  other  s-econd-chromosome  mutant 
except  vestigial.     Its  viability  also  is  excellent. 

APTEROUS  (a,). 

(Plate  7,  figure  5.) 

ORIGIN  OF  APTEROUS. 

The  mutant  called  ''apterous"  was  first  found  by  Miss  Wallace  in 
the  white  miniature  stock  in  August  1913.  This  form  continued  to 
appear  as  occasional  individuals,  both  males  and  females,  for  some 
months,  from  which  it  was  concluded  that  the  mutant  was  an  autosomal 
recessive  for  which  only  a  few  white  miniature  flies  were  heterozygous. 
Several  attempts  to  breed  apterous  individuals  to  one  another  or  to 
other  flies  failed,  and  it  was  thought  that  the  form  was  completely  sterile. 

DESCRIPTION  OF  APTEROUS. 
The  most  striking  feature  of  this  mutant  is,  as  its  name  implies,  the 
total  absence  of  wings,  the  vestiges  being  in  most  cases  a  mere  rough- 
ness. The  balancers  also  are  reduced  in  the  same  manner  as  the  wings, 
a  condition  that  was  first  found  in  the  case  of  vestigial.  The  apterous 
flies  are  small  in  size,  rather  pale  in  color,  and  markedly  sluggish  in 
movement;  they  easily  become  entangled  in  food  or  cotton  and  drown 
or  dry  up.  Even  when  kept  very  carefully  under  the  best  conditions 
they  seldom  live  more  than  three  or  four  days. 

INHERITANCE  OF  APTEROUS. 

At  this  stage  Metz  (C.  W.  Metz,  Am.  Nat.  1914,  pp.  675-692)  began 
work  with  the  mutation  and  found  that  the  failure  to  breed  was  largely 
because  the  males  were  too  weak  to  copulate  and  the  females  pro- 
duced few  or  only  rudimentary  eggs.  In  only  three  cases  out  of  more 
than  a  hundred  did  apterous  females  give  offspring  when  crossed  to 
normal  males,  and  there  was  correspondingly  only  a  single  case  of 
fertilization  by  an  apterous  male.  From  these  crosses  and  from 
inbreeding  other  pairs  heterozygous  for  apterous  there  were  produced 
a  total  of  1,405  wild-type  to  450  apterous  flies,  or  24.3  per  cent  apter- 
ous, which  is  a  remarkably  close  approach  to  expectation,  in  spite  of 
the  weakness  of  the  apterous  flies. 


OF   MUTANT   CHARACTERS.  237 

CHROMOSOME  CARRYING  APTEROUS. 

Metz  crossed  an  apterous  male  to  a  vermilion  female  and,  as  ex- 
pected, the  apterous  character  and  vermilion  showed  no  linkage  in  Fj. 
The  total  offspring  from  pair  matings  in  this  line  was  1,49S  wild-t^-pe 
to  369  apterous,  or  19.8  per  cent,  which  is  a  poorer  viability  than 
before,  but  not  as  low  as  in  the  sister  culture  raised  en  masse.  The 
mass-cultures  gave  only  699  apterous  among  4,539  offspring,  and  the 
low  percentage  (15.4)  is  the  result  of  the  crowding  that  always  occurs 
in  mass-cultures. 

An  apterous  female  was  successfully  crossed  to  a  pink  male  and 
there  were  produced  in  F2  402  wild-tj^De,  114  apterous.  111  pink,  and 
34  apterous  pink  flies,  which  is  an  approach  to  a  9:3:3:1  ratio  and 
proved  that  apterous  was  not  third-chromosome. 

No  successful  mating  of  apterous  by  black  was  made,  so  that  flies 
heterozygous  for  apterous  had  to  be  used  in  the  Pi  instead.  From 
Fi  pairs,  heterozygous  for  apterous  in  both  parents,  there  were  pro- 
duced 414  wild-type,  136  apterous,  155  black,  and  0  black  apterous 
flies.  This  2:1:1:0  ratio  demonstrated  that  apterous  is  in  the  second 
chromosome. 

LOCUS  OF  APTEROUS. 

In  determining  the  locus  of  apterous,  Metz  took  advantage  of  the 
fact  that  flies  heterozygous  for  black  are  darker  than  the  wild-tj-pe, 
that  is,  he  classified  black  as  a  dominant  as  well  as  a  recessive  character 
in  F2.  In  the  above  F2  from  the  cross  of  apterous  (heterozygous)  to 
black,  Metz  observed  no  apterous  flies  that  seemed  to  be  heterozygous 
for  black  and  correspondingly  no  long- winged  flies  that  were  not 
heterozygous  for  black.  While  this  classification  can  not  be  accurate, 
it  is  nevertheless  certain  that  if  very  many  such  cross-over  flies  had 
been  present  this  fact  could  have  been  noted.  The  locus  of  apterous 
is  therefore  not  far  from  that  of  black  in  the  second  chromosome. 

APTEROUS  BY  REMUTATION. 

In  working  with  the  eosin  modifier  "cream  c"  Bridges  found  a 
mutant  character  which  in  appreance  agreed  at  every  point  with  the 
previously  known  apterous  (cultures  5588,  5631,  October  16,  1916). 
This  experiment,  in  which  apterous  reappearance  had  come  from  the 
Pi  mating  of  the  original  cream  c  female  (found  in  eosin  stock)  and  a 
star-dichaete  male  (dichsete  is  a  third-chromosome  dominant).  The 
Fi  mating  had  been  of  (eosin)  star-dichaete  sons  and  wild-tyi)e  daugh- 
ters in  pairs.  The  apterous  character  appeared  in  63  individuals 
(males  and  females  equally  numerous)  in  a  total  of  449  in  two  sei)arate 
cultures  (5588  and  5631).  The  percentage  of  apterous  was  thus  only 
14.0,  which  indicates  a  rather  poorer  viabihty  than  was  shown  in  the 
culture  of  Metz. 


238 


THE    SECOND-CHROMOSOME    GROUP 


CHROMOSOME  CARRYING  APTEROUS. 
The  apterous  character  was  distributed  at  random  with  respect  to 
both  eosin  (first  chromosome)  and  dichsete  (third  chromosome) .  Not 
one  of  the  star  F2  indi\dduals  was  apterous.  In  fact,  the  F2  ratio  of 
258  star  :  128  wild-type  :  63  apterous  :  0  star  apterous  approached 
the  2:1  : 1  : 0  ratio  expected  if  apterous  is  in  the  second  chromosome 
(table  86).     There  was  observed  a  very  free  crossing-over  between 

Table  86. — Pi,  cream  c    9    {heterozygous  for   apterous)    X    star  dichcete   cT; 

Fi  wild-type   9    +  Fi  star  dichoete  cf . 


Oct.  20,  1916. 

Star. 

Wild- 
type. 

Apter- 
ous. 

Star 
apterous. 

5588 

5631 

104 
154 

67 
61 

37 
26 

0 
0 

Total 

258 

128 

63 

0 

cream  c  and  apterous,  and  this  fact,  in  connection  with  the  star  apter- 
ous result,  proved  that  the  apterous  mutation  had  been  present  in  the 
cream  c  female,  which  was  presumably  heterozygous  for  it.  That  this 
appearance  of  apterous  is  due  to  a  second  and  independent  occurrence 
of  the  act  of  mutation  in  the  apterous  locus  can  not  be  doubted. 


+' 


Table  87.— F2,  F3  and  F^  star  9  (jr~-)  +  ^2,  Fs,  and  F4  wild-type  cf  (- ) 


Nov.  18.  1916. 

Star. 

Wild- 
type. 

Apter- 
ous. 

Star 
apterous. 

5834 

95 

3 

57 

95 

5 

60 

24 
6 

9 
1 
3 

6014 

6070 

Total 

155 

160 

30 

13 

S'4- 


Table  SS.—FiStar  9   r-T-^^+  Fi  star  &  (^r-^^ 

V+  aJ  \-\-  aJ 


Jan.  1.  1917. 

Star. 

Wild- 
type. 

Apter- 
ous. 

Star 
apterous. 

6347 

24 

6 

7 

9 

LOCUS  OF  APTEROUS. 
An  opportuinty  for  determining  the  locus  of  apterous  was  provided 
by  the  above  material.     All  attempts  to  back-cross  the  F2  star  females, 
a  majority  of  which  were  heterozygous  for  apterous, 

(^:-±\ 

\+       Op/ 

by  apterous  males  failed  as  expected,  because  of  the  sterility  of  the 
apterous  males.     However,  a  few  matings  between  such  females  and 


OF    MUTANT    CHARACTERS.  239 

wild-type  brothers  heterozygous  for  apterous  succeeded  (table  87). 
There  were  produced  a  total  of  358  flies,  of  which  only  43  or  12.0  per 
cent  were  apterous.  Of  these  43  the  star  apterous  cross-overs'^  num- 
bered 13  and  the  simple  apterous  non-cross-overs  30. 

These  flies  are  comparable  in  viability  and  the  percentage  of  cross- 
ing over  can  be  calculated  directly  from  them  as  30.2.  Another 
calculation  can  be  made  from  the  not-apterous  flies,  of  which  there 
were  155  stars  and  IGO  wild-type.  Both  these  classes  are  comjiosite, 
the  stars  comprising  two  non-cross-over  and  one  cross-o\'er  clas.s 
(2n-f  X  =  155),  while  the  wild-type  flies  comprise  one  non-cross-over  and 
two  cross-over  classes  (n-f2x  =  160).  From  these  equations  n  =  50 
x  =  55,  or  the  percentage  of  crossing  over  is  52.3. 

One   cross   of   star   female    by  star   male   both  (*— )  produced 

offspring  only  one  of  whose  classes  is  composite  (table  88).  As  before, 
the  star  apterous  flies  are  cross-overs  {x  =  9)  and  the  apterous  non- 
cross-overs  (n  =  7)  which  gives  9  cross-overs  out  of  16  or  50  per  cent. 
The  wild-type  class  is  a  simple  non-cross-over  (n  =  6)  to  be  compared 
with  the  complex  class  star  (2n+x  =  24).  From  these  equations 
x  =  6  and  n  =  9,  or  the  percentage  of  crossing  over  is  40.0.  The  total 
amount  of  crossing-over  data  derived  above  gives  the  equivalent  of 
169  flies,  of  which  83  or  49.0  per  cent  are  cross-overs.  From  a  com- 
parison of  this  value  (49.0)  with  the  cross-over  values  given  by  star 
and  other  second-chromosome  genes,  the  locus  of  apterous  is  found  to 
be  most  probably  somewhat  to  the  right  of  black.  This  locus  agrees 
perfectly  with  the  position  found  by  Metz  on  the  basis  of  the  black- 
apterous  F2  described  above.  A  position  at  48.5  is  indicated  as  approxi- 
mately correct. 

Cii,  AND  Cii, 

A  paper  by  Sturtevant,  giving  a  full  account,  with  summaries,  of  the 
work  done  on  the  two  second-chromosome  cross-over  variations  Cm 
and  Cii,  appears  herewith  (Part  III),  to  which  the  reader  is  referred. 

CREAM  II  (Cru)} 

(Plate  5,  figure  11.) 

ORIGIN  AND  DESCRIPTION  OF  CREAM  II. 

A  pure  stock  of  the  sex-linked  eye-color  eosin  shows  a  strong  sexual 
bicolorism;  that  is,  the  eye-color  of  the  eosin  female  is  a  rather  deep 
pink  only  slightly  yellowish,  while  the  eye-color  of  the  eosin  male  is  a 
pinkish  yellow  much  lighter  in  tone  than  the  color  of  the  female  (see 
Morgan,  1912,  for  an  account  of  the  origin  of  eosin  and  a  colored  plate 
showing  this  difference  in  color).     Eosin  females  and  males  maintain 

*  A  short  reference  to  the  case  of  cream  II,  and  a  discussion  of  its  bearinK  on  the  queation  of 
multiple  factors  was  made  in  the  "Mechanism  of  Mendelian  Heredity,"  p.  203. 


240  THE    SECOND-CHROMOSOME    GROUP 

this  constant  difference  in  color  wherever  they  reappear  after  crossing, 
and  all  double  recessives  involving  eosin,  for  example,  eosin  vermilion 
and  eosin  pink,  are  likewise  bi-colored  (Morgan  and  Bridges,  1913). 

In  caiTj'ing  on  a  stock  of  non-disjunction  by  means  of  eosin.  Bridges 
found  (July  13,  1913)  that  certain  flies  were  showing  an  eye-color 
considerably  paler  than  the  standard  eosin.  Investigation  of  these 
"  cream"-colored  flies  showed  that  they  were  double  recessives,  being 
eosin  plus  a  specific  modifer  of  eosin  eye-color.  Thus,  a  pure  stock 
of  the  modifier  would  look  precisely  like  a  stock  of  wild  flies. 

Shortly  after  the  discovery  of  the  first  cream  (cream  a),  a  second 
cream  appeared  (September  15,  1913)  among  the  eosin  males  and 
females  of  a  stock  culture  of  lethal  2}  Wild- type  females  heterozy- 
gous for  lethal  2  had  been  crossed  to  eosin  miniature  males,  and  the 
Fi  wild- type  daughters  again  crossed  to  eosin  miniature  males.  The 
mothers  of  the  culture  which  gave  the  creams  were  therefore  wild- 
type  females  heterozygous  for  eosin  and  miniature  as  well  as  lethal  2 

(+ 1+)>  while  the  fathers  were  eosin  miniature.  The  cream  males 
and  females  which  appeared  were  much  paler  than  cream  a,  though 
like  cream  a  they  were  a  light,  translucent  yellow  with  little  or  no 
pinkish  tinge.  None  of  the  not-eosin  flies  were  different  in  color 
from  normal  red  flies. 

A  careful  examination  of  the  stock  of  eosin  miniature  failed  to  show 
any  flies  that  did  not  have  the  standard  eosin  eye-color,  and  no  Ughter 
eye-color  has  ever  subsequently  shown  itself  in  this  stock.  It  is  evi- 
dent that  the  gene  for  the  modification  had  been  present  in  the  wild- 
type  flies  of  the  lethal  2  stock,  but  had  been  unsuspected  so  long  as 
eosin  was  not  present  as  a  base.  The  demonstration  that  the  cause 
of  the  observed  dilution  of  eosin  w^as  a  gene  behaving  in  inheritance 
like  the  other  mutant  genes  was  easily  made. 

INHERITANCE  OF  CREAM  II. 
One  of  these  cream  males  w^as  out-crossed  to  a  wild  female.  Among 
the  F2  flies  the  creams  reappeared,  and,  as  in  the  parallel  case  of  cream 
a,  the  not-eosin  flies  were  all  indistinguishable  from  one  another  and 
from  w^ld  flies  in  color.  The  F2  result  resembles  that  obtained  with 
cream  a,  except  that,  as  stated,  the  new  cream  was  considerably  paler ; 
and  it  was  further  discovered  that  besides  the  creams,  approximately 
50  per  cent  of  the  eosin  males  were  intermediates  between  eosin  and 
this  cream,  that  is,  cream  II  diluted  eosin  even  in  heterozygous  form, 
so  that  the  eosin  sons  were  visibly  as  well  as  genetically  in  the  ratio 
1  eosin  :  2  eosin  heterozygous  for  cream  II  :  1  eosin  pure  for  cream  II. 
The  entire  ratio,  disregarding  sex,  approximated  12:1:2:1,  the  12 
being  the  red-eyed  flies. 

'This  culture  was  part  of  a-generation  which  succeeded  generation  Q,  table  22,  p.  Ill,  Morgan, 
1914,  and  which  gave  results  similar  to  the  results  of  generations  J  to  Q  of  table  22. 


OF    MUTANT    CHARACTERS. 

STOCK  OF  CREAM  II. 


'2U 


From  the  F2  a  few  cream  males  were  selected  and  bred  to  their 
sisters,  all  of  which  were  wild-t^-pe  in  appciirance,  though  a  quiirter 
of  them  were  homozygous  for  the  cream  gene  (not-eosin  creams). 
This  mass-culture  gave  the  expect-ed  cream  femiiles  and  niiiles,  from 
which  a  pure-breeding  stock  was  made  up.  There  was  a  difTeronce 
in  the  color  of  the  males  and  females  of  this  pure  stock,  the  difference 
being  of  the  same  order  as  the  normal  bicolorism  of  eosin, 

A  complete  separation  of  the  eosin  from  the  eosin  heterozygous  for 
cream  had  not  been  attempted  in  the  original  F2  culture.  In  order  to 
observe  the  heterozygous  condition  more  closely  a  cream  male  from 
the  pure  stock  was  out-crossed  to  an  eosin  female.  The  Fi  flies  both 
males  and  females  (culture  M  68,  intermediate  males  73,  intermedmte 
females  88)^  were  hghter  in  eye-color  than  standard  eosin,  though  the 
difference  between  eosin  and  these  heterozygotes  was  less  than  the 
difference  between  the  heterozygotes  and  the  pure  cream. 

Table  89. — ^^2  offspring  from  the  cross  of  a  cream  male  to  an  eosin  female. 


Dec.  6,  1913. 

Females. 

Males. 

Eosin. 

Hetero- 
zygous 
cream. 

Cream. 

Eosin. 

Hetero- 
zygous 
cream. 

Cream. 

M  77 

30 
19 
23 
14 

57 
49 
43 
32 

29 
16 
19 
11 

29 

14 
18 
13 

46 
30 
34 
27 

25 
15 
20 
13 

M  78 

M  79 

M  95 

Total 

86 

181 

75 

74 

137 

73 

Among  these  F2  offspring  (table  89)  there  were  six  different  eye- 
colors;  among  the  males,  the  same  three  that  occurred  in  the  original 
F2,  and  among  the  females  three  colors  which,  though  corresponding 
genetically  to  the  classes  among  the  males,  were  darker  in  eye-color. 
The  cream  female  is  lighter  than  the  eosin  male,  while  the  het-erozy- 
gous  cream  female  is  somewhat  darker  than  the  eosin  male.  In  order 
from  the  darkest  (a  deep  slightly  yellowish  pink)  to  the  lightest  (a 
pale  translucent  yellow)  the  six  colors  are:  eosin  female,  heterozygous 
cream  female,  eosin  male,  heterozygous  cream  male,  cream  female, 
cream  male.     The  females  were  first  separated  from  the  males.     Then 

*  One  of  the  88  intermediate  daughters  had  only  three  segments  to  her  alxlomen  instoiwl  of  tho 
usual  five.  This  female  (figured  by  Morgan,  1915,  p.  425,  text-figure  3a)  was  the  founder  of  a 
new  type  of  abnormal  segmentation  of  the  abdomen — "patched."  The  segment^j  wore  rwiucwl 
in  number  (as  in  the  first  specimen),  or,  more  typically,  were  cut  sharply  inU)  obliciuo  or  triangular 
pieces  which  were  patched  together  as  illu.strated  in  figures  h  to /,  of  plate  11.  This  charucter 
was  recessive,  t)Ut  it  generally  reappeared  in  very  much  less  than  a  (piarter  of  the  I'l  ofT.tpring. 
The  usual  causes  for  such  deficiencies  are  poor  vial)ility,  parti;U  or  conjploto  doiM'iuiencc  for 
realization  on  the  coaction  of  one  or  more  other  genes,  or  failure  to  be  developed  in  all  the  flies 
fluctuations  of  pure  for  the  gene,  whether  from  environmental  differences  or  because  the  normal 
genetically  the  character  overlap  the  wild-type.  The  gene  for  patched  waa  in  the  second  chro- 
mosome, as  shown  by  its  strong  linkage  to  the  cream. 


242  THE   SECOND-CHROMOSOME    GROUP 

in  each  sex  the  pure  creams  were  separated  from  the  others,  and 
finally  the  more  difficult  separation  of  heterozygous  cream  from  eosin 
was  undertaken.  The  separation  of  the  creams  from  the  other  colors 
is  -accurate,  but  the  final  separation,  that  of  the  heterozygous  creams 
from  the  eosins,  must  be  regarded  as  only  a  close  approximation. 
The  sharp  1:2:1  ratio  (160:318:148)  which  was  obtained  from 
this  separation  probably  represents  among  the  eosins  a  small  number 
of  the  darkest  heterozygotes,  while  the  lightest  of  the  pure  eosins  were 
likewise  classified  among  the  heterozygotes.  Probably  10  per  cent 
of  the  combined  eosin  and  heterozygous  cream  class  overlapped  enough 
so  that  the  separations  might  or  might  not  correspond  to  genetic 
differences.  One  test  of  the  correctness  of  the  classification  of  inter- 
mediates was  made.  From  culture  M  79  a  heterozygous  male  and  a 
heterozj^gous  female  were  selected,  and  the  results  (culture  M  75) 
showed  that  both  individuals  were  of  the  supposed  type. 

No  attempt  has  been  made  to  secure  a  stock  homozygous  for  the 
cream  gene  but  without  eosin.  The  cultures  and  experiments  in 
which  such  not-eosin  creams  must  have  constituted  one-fourth  of  the 
wild-type  flies  prove  that  such  a  stock  could  not  be  distinguished  by 
inspection  from  a  wild  stock. 

That  the  action  of  cream  II  is  specific  to  eosin  was  suggested  by 
crosses  of  cream  with  vermilion  (X  chromosome)  and  with  pink  (third 
chromosome).  A  careful  examination  of  the  F2  flies  from  these 
crosses  showed  no  dilution  of  either  vermilion  or  pink  by  the  cream,  that 
is,  the  double  recessives  vermilion  cream  and  pink  cream  (not-eosin) 
are  indistinguishable  from  vermilion  and  pink  respectively. 

LINKAGE  METHOD  OF  ANALYSIS  FOR  MULTIPLE-GENE  CASES. 

The  proper  method  of  study  for  cases  of  multiple  factors  or  of  modi- 
fiers is  by  means  of  linkage  experiments,  whereby  all  guesswork  as 
to  the  number  and  effect  of  modifiers  can  be  eliminated.  In  Dro- 
sophila  such  a  study  is  rendered  particularly  easy  by  the  fact  that  in 
the  male  there  is  no  crossing-over  of  any  of  the  chromosomes.  In  con- 
sequence, if  two  recessive  genes  which  belong  to  the  same  chromosome, 
e.  g.,  black  and  vestigial  of  the  second  chromosome,  enter  the  cross 
from  opposite  parents  ("repulsion"),  the  F2  never  shows  flies  which 
have  both  these  mutants  at  the  same  time.  The  double  recessive 
class  is  entirely  unrepresented,  and  the  2:1:1:0  ratio  of  ''absolute 
repulsion"  results.  This  ratio  holds,  whatever  may  be  the  amount  of 
crossing-over  in  the  female,  for  the  lack  of  double-recessive  sperm 
prevents  the  double-recessive  eggs  from  revealing  themselves.  This 
ratio  is  in  marked  contrast  to  the  9:3:3:1  ratio,  which  obtains  when 
the  two  genes  belong  to  different  chromosomes,  e.  g.,  curved  of  the 
second  chromosome  and  ebony  of  the  third  chomosome. 

The  light  color  cream  was  known  to  be  eosin  plus  a  recessive  modifier 
which  belonged  to  an  autosome  group.     To  find  whether  this  group 


PLATE  11 


m  # 


■^ 


J 


OF    MUTANT    CHARACTERS. 


243 


was  that  of  the  second  chromosome,  a  cream  nmle  (from  pure  stock) 
was  out-crossed  to  a  curved  female,  curved  being  a  recessive  wing- 
character  whose  gene  is  known  to  belong  to  the  second  chromosome 
(Bridges  and  Sturtevant,  1914).  A  pair  of  Fi  wild-type  flies  inbred 
gave  the  results  of  table  90. 

Table  90.— F^  from  the  cross  of  cream  II  male  to  curved  female. 


Feb.  20,  1914. 

Not-nosin  (cf  +  9). 

Eosin  (males  only). 

Wild- 
type. 

Curved. 

Eosin. 

Eosin 
curved. 

Cream  II. 

Cream  II 
curved. 

70 

155 

04 

37 

14 

15 

0 

Since  cream  only  shows  itself  where  eosin  is  already  present,  we  may 
disregard  all  the  flies  of  culture  70  except  those  with  eosin  eyes.  Tho^ 
eosin  flies  are  obviously  in  the  ratio  2:1  : 1  :0  which  is  expected  if  the 
cream  gene' is  in  the  second  chromosome,  through  the  flies  are  too  few 
to  prove  the  point. 

Table  91. — Pi,  cream  II  d*  X  eosin  black  9  .    Fi  heterozygous 
cream  9    X  Fi  heterozygous  cream  cf . 


Fi  cultures. 
Mar.  16.  1914. 

Heterozygous 
cream  9  9  • 

HeterozyKOUS 
cream  c?cf. 

119 

51 
15 

41 

18 

329 

Total .... 

66 

59 

F2  cultures. 
Aug.  3,  1914. 

Eosin. 

Eosin  black. 

Cream  II. 

Black  cream  II. 

9 

cf 

9 

d" 

9 

d' 

9 

d' 

372 

50 
57 
69 

48 

38 
42 
79 
59 

24 
18 
36 
33 

15 
31 
43 
17 

14 
19 
43 
24 

25 
19 
39 
24 

0 
0 
0 
0 

0 
0 
0 
0 

398 

399 

400 

Total .... 

224 

218 

111 

106 

100 

107 

0 

0 

442 

217 

207 

0 

A  more  efficient  experiment  than  this  last  was  carried  out  by  making 
all  the  flies  of  the  experiment  eosin,  in  which  case  the  2:1  : 1 : 0 
ratio  involved  all  the  offspring  rather  than  only  a  quarter,  as  in  culture 
70.  A  stock  of  eosin  black  was  made  up  (black  being  a  second-chro- 
mosome mutant)  and  a  female  of  this  stock  was  outcrossod  to  a  cream 
II  male.  The  Fi  and  F2  results  are  given  in  table  91.  All  of  the  Fi 
flies  and  half  the  F2  flies  were  of  the  intermedLate  color  of  the  het<:'rozy- 
gous  cream.  In  the  F2  these  intermediates  were  classified  along  with 
the  pure  eosins,  so  that  the  cream  was  treated  as  though  a  strict 
recessive. 


244 


THE    SECOND-CHROMOSOME    GROUP 


The  F2  ratio  of  442  :217  :  207  :0  is  a  very  close  approximation  to  a 
2:1:1:0  ratio  and  proves  that  the  gene  for  cream  is  in  the  second 
chromosome  (cream  II). 

A  similar  experiment  in  which  cream  was  crossed  to  eosin-ebony 
(ebony  being  a  third-chromosome  mutant,  see  Stiirtevant,  1914)  gave 
a  typical  9:3:3:1  ratio  (table  92),  which  agrees  with  the  fact  that 
the  cream  gene  is  not  in  the  third  chromosome. 

Table  92. — F^,  from  the  cross  of  cream  II  cf  hy  eosin  ebony  9  . 


Mar.  31, 1914. 

Eosin. 

Cream  II. 

Eosin 
ebony. 

Cream  II 
ebony. 

154 

61 

85 
134 

21 

28 
37 

18 
35 
36 

4 
14 
10 

161 

162 

Total... 

280 

86 

89 

28 

In  order  to  find  the  locus  of  cream  within  the  second  chromosome 
it  would  have  been  necessary  to  run  two  linkage  experiments  in  which 
all  the  flies  were  eosin;  thus,  one  of  these  might  have  been  cream  II 
by  eosin  black  and  a  back-cross  of  the  Fi  female  to  black  cream  males, 
and  the  other  a  similar  back-cross  in  which  curved  was  used  in  place 
of  black.  The  amount  of  crossing-over  between  black  and  curved  was 
known  to  be  about  27  per  cent.  The  two  values  black  cream  and 
curved  cream  which  would  be  found  by  two  such  experiments  (both 
values  might,  of  course,  be  found  from  a  single  suitably  devised  experi- 
ment) would  enable  the  locus  of  cream  to  be  calculated  with  consid- 
erable accuracy.  While  much  is  to  be  learned  of  the  mechanism  of 
crossing-over  from  a  study  of  the  relative  distributions  of  loci  within 
various  regions  of  the  chromosome,  yet  in  the  case  of  cream  II  it  was 
thought  that  the  compensation  would  not  be  worth  the  effort.  Any 
further  use  of  cream  II  in  other  linkage  experiments  would  involve 
the  "  eosinization  "  of  all  the  stocks  used.  In  the  case  of  certain  of  the 
later  creams,  an  approximate  location  of  the  gene  within  the  chromo- 
some has  been  made,  but  such  location  was  made  easier  by  the  dis- 
covery of  certain  dominant  mutations  which  were  not  available  at 
the  time  the  work  on  cream  II  was  finished. 

TREFOIL  (//). 

(Plate  5,  fig.  6;  plate  8,  fig.  1.) 

ORIGIN  AND  STOCK  OF  TREFOIL. 

The  character  trefoil  was  found  by  Morgan  about  November  1913, 
and  a  pure-breeding  stock  was  secured  without  difficulty. 

DESCRIPTION  OF  TREFOIL. 
The  character  trefoil  is  quite  variable  in  the  intensity  of  pigmenta- 
tion, as  is  the  case  with  all  of  the  thorax  pattern  characters.     The 


OF   MUTANT    CHARACTERS.  245 

distribution  of  the  pigment  is  very  definite,  however.  The  scut^^lhim 
is  largely  or  entirely  dark  and  the  base  of  the  trident  pattern  on  the 
thorax  is  broader  and  much  heavier,  while  the  prongs  are  scarcely 
darkened  at  all.  The  characteristic  feature  of  trefoil  is  tlie  presence 
of  extra  basal  sections  to  the  trident  outside  the  regular  region.  These 
side  areas  are  fully  as  dark  as  the  central  parts  and  extend  forward 
even  farther.  Another  region  that  is  dark  in  trefoil  but  not  in  the 
other  thorax  patterns  is  a  patch  behind  each  eye  on  the  back  of  the 
head.  These  eye-patches  and  the  side-prongs  are  the  niiiin  characters 
used  in  classifying  trefoil. 

INHERITANCE  OF  TREFOIL. 

In  out-crosses  to  wild,  trefoil  behaved  as  an  autosomal  recessive, 
giving  only  wild-type  flies  in  Fi,  and  reappearing  as  about  a  quarter 
of  the  F2  flies. 

CHROMOSOME  CARRYING  TREFOIL. 

F2  from  the  cross  of  trefoil  to  pink  gave  a  9  : 3  : 3  :  1  ratio,  while 
the  corresponding  cross  to  curved  gave  a  2  : 1  : 1  :  0  ratio,  from  which 
it  was  seen  that  the  locus  of  trefoil  is  in  the  second  chromosome. 

LOCUS  OF  TREFOIL. 

It  was  found  that  trefoil  and  black  together  gave  a  very  dark  fly 
which  was  distinguishable  from  black.  With  some  difficulty  a  triple- 
recessive  black  strap  trefoil  stock  was  made  up  to  test  the  locus  of  tre- 
foil. This  stock  was  never  used,  but  from  the  indications  met  with  in 
its  synthesis  it  seemed  probable  that  the  locus  of  trefoil  is  not  far  from 
that  of  black,  but  between  black  and  strap.  This  was  confirmed 
roughly  by  a  star  trefoil  back-cross  which  gave  42.1  per  cent  of  crossing- 
over  (S  34,  tf  55,  S  tf  42,  -f23).  The  locus  is  thus  at  about  50.0 
with  reference  to  star. 

VALUATION  OF  TREFOIL. 

Considerable  difficulty  was  met  with  in  the  classification  of  trefoil 
from  the  variability  of  the  character,  and  for  this  reason  there  was  no 
strong  incentive  to  establish  its  locus  or  to  use  it  in  any  way. 

CREAM  b  (cj. 

(Plate  5,  fig.  11.) 

ORIGIN  OF  CREAM  b. 

An  eosin  female  from  a  stock  of  non-disjunction,  when  mated  to  a 
bar  male,  gave  (culture  82,  March  10,  1914)  among  the  eosin  sons  one 
whose  eye-color  was  as  light  as  tliat  of  cream  II  or  cream  III.  This 
male  was  out-crossed  to  a  wild  female  and  in  Fo  gave  creams  among 
the  eosin  sons  but  no  disturbance  of  the  color  of  the  not -eosin  flies 
(cultures  183, 184, 185).     The  F2  ratio  was  again  12  :  3  :  1,  as  in  similar 


246 


THE    SECOND-CHROMOSOME    GROUP 


crosses  with  other  recessive  specific  dihitors.  But  the  creams  (cream 
b)  which  occurred  in  this  F2  were  not  as  pale  as  any  of  the  preceding 
creams. 

From  the  circumstances  of  the  appearance  of  cream  b,  viz,  that  it  was 
observed  in  the  Fi  of  an  out-cross  and  that  as  a  single  individual,  we 
should  expect  it  to  be  a  dominant,  but  as  a  matter  of  fact  it  proved  to 
be  a  recessive.  It  seems  probable,  in  explanation,  that  more  creams 
were  actually  present  in  this  Fi  but  were  overlooked,  since  attention 
was  distracted  by  the  simultaneous  appearance  in  the  same  culture  of 
still  another  mutation  (lethal  4),  and  more  especially  since  the  effect 
of  cream  b  is  rather  slight.  Only  occasionally  was  one  of  the  F2  creams 
so  marked  as  the  grandfather,  and  the  mutation  might  not  have  been 
recognized  at  all  were  it  not  that  an  extreme  fluctuant  had  attracted 
attention.  Since  cream  b  is  recessive,  we  must  suppose  that  the  gene 
was  present  in  both  parent  stocks.  It  could  have  been  present  in  the 
bar  stock  and  been  undetected  becausp  of  the  lack  of  eosin,  without 
which  it  has  no  visible  effect;  and  the  character  might  readily  have 
been  present  in  the  eosin  non-disjunction  stock  and  have  been  passed 
over  as  an  age  variation,  since,  as  we  ordinarily  see  flies  from  a  stock 
culture,  they  are  of  all  ages  and  of  all  corresponding  densities  of  pig- 
mentation. 

CHROMOSOME  CARRYING  CREAM  b. 

A  pure-breeding  stock  was  made  up  for  use  in  back-crossing.  By 
this  time  we  were  in  possession  of  a  good  second-chromosome  domi- 
nant "star"  and  likewise  of  a  perfect  third-chromosome  dominant 

Table  93. — B.  C.  offspring  from  the  Pi  mating  of  an  eosin  star  dichceie  male  to 
a  cream  b  female  and  the  hack-crossing  of  the  Fi  eosin  star  dichcete  male 
to  cream  b  females. 


Sept.  8,  191G. 

Non-cross-overs. 

C 

ross-overs 

(in  male). 

Eosin 
star. 

Eosin 

star 

dichsete. 

Cream  b. 

Cream  b 
dichsete. 

Star 
cream  b 

Star 
cream  b 
dichsete. 

Eosin. 

Eosin 
dichsete. 

^^?::";;;.:::: 

20 
19 
14 
14 

25 
21 
21 
15 

26 
21 

18 
17 

12 
26 
26 
24 

0 
0 
0 
0 

0 
0 
0 
0 

0 
0 
0 
0 

0 
0 
0 
0 

Total 

67 

82 

82 

77 

0 

0 

0 

0 

"dichsete,"  which  mutants  have  now  become  the  most  important  in 
their  respective  chromosomes.  By  aid  of  these  two  dominants  it  is  very 
easy  to  determine  in  a  single  experiment  whether  a  given  mutant  is  in 
the  second  or  third  chromosome.  Thus,  in  the  case  of  cream  b,  a  stock 
of  eosin  star  dichsete  was  made  up  and  used  in  making  a  Pi  cross  to  the 
cream.  Then  Fi  eosin  males  which  showed  both  star  and  dichsete  and 
which  were  heterozygous  for  the  recessive  cream  were  back-crossed 


c    « 


«  «  i  ( 

«  •  •  •  t 

&      «      «  1    (  •  4 

C     «      <        k  i        <  W  I 

*         *   t  •>  1  «  «  I 


«    '     ' '      .    •  «     ' 


OF    MUTANT    CHARACTERS. 


247 


to  cream  b  females  of  stock.  There  is  no  crossing-over  in  the  male  of 
Drosophila,  so  that  if  cream  b  were  in  the  second  chromosome  not 
one  of  the  B.  C.  star  offspring  should  be  cream,  while  liiilf  of  the 
dichsete  should  be  cream  and  half  not.  If,  on  the  other  liand,  the 
cream  were  in  the  third  chromosome,  then  none  of  the  h.  ('.  dichu't^'S 
should  be  cream,  while  the  star  and  cream  should  assort  at  random. 
The  experiment  proved  that  the  gene  for  cream  b  is  in  the  second 
chromosome  (table  93). 

LOCUS  OF  CREAM  b. 

An  (eosin)  star  female  and  a  cream  b  male  selected  from  the  B.  C. 
offspring  gave  in  the  next  generation  the  amount  of  crossing-over 
between  star  and  cream  b  (table  94).  This  value  of  22.1  includes  some 
double  crossing-over,  and  the  corrected  or  "map"  distance  is  probably 
about  22.5.  The  chances  are  in  favor  of  the  cream  b  locus  being  to 
the  right  of  star,  since  star  happens  to  occupy  the  leftmost  of  the  known 
loci. 

Table  94. — B.  C.  offspring  given  in  F3  by  an  eosin  star  female 
and  a  cream  b  male  from  table  93. 


Non-cros.s-overs . 

Cross-overs 
(in  female). 

Oct.  2u,  lyio. 

Eosin 
star. 

Cream  b. 

Star 
cream  b. 

Eosin. 

5593< 
6532< 

r? 

^9 

.cf 

36 
22 
47 

28 

41 
41 
39 
49 

8 
12 
13 
11 

8 
12 

i 

15 

r 

rotal.... 

1.33 

i7e 

44 

42 

PINKISH. 

(Plate  5,  fig.  12.) 

ORIGIN  OF  PINKISH. 

In  the  fall  of  of  1913  a  stock  of  eosin  black  had  been  made  up  with 
which  to  test  the  chromosome  group  of  cream  II.  In  the  following 
summer  (July  27,  1914)  Bridges  noticed  that  a  few  of  the  males  were 
somewhat  lighter  in  eye-color  than  the  others,  but  seemed  chiefly 
noticeable  because  of  the  weakness  of  the  yellow  component  of  the 
eosin  eye-color.  The  color  of  the  regular  eosin  male  is  a  pinkish 
yellow;  the  color  of  cream  a,  II,  III,  and  b  is  nearly  a  pure  yellow  with 
httle  of  the  pinkish  tinge,  while  this  new  color  was  somcwliat  the 
converse  of  this  and  was  a  pale  pink  with  relatively  little  yellow. 

One  of  these  males  mated  to  a  sister  gave  all  of  the  sons  of  this 
pinkish  color  and  all  the  daughters  of  a  similar  color,  which  is,  however, 
much  harder  to  distinguish  from  standard  eosin.  It  seems  that  this 
character  is  somewhat  sex-limited  in  the  siune  direction  jls  eosin. 


248 


THE    SECOND-CHROMOSOME    GROUP 


Pure  stock  of  the  mutation  had  been  obtained  at  once  through  the 
happy  selection  of  a  pure  pinkish  female  which  had  been  taken  to  be 
simply  an  eosin  female  of  somewhat  lighter  eye-color  because  of 
being  freshly  hatched. 

CHROMOSOME  CARRYING  PINKISH. 

Since  pinkish  appeared  in  a  stock  of  eosin  black,  material  was  on 
hand  to  test  the  chromosome  group  at  once.  Accordingly,  black 
pinkish  females  were  out-crossed  to  eosin  males  and  the  F2  eosin 
jfemales,  standard  eosin  in  color,  were  back-crossed  to  black  pinkish 
males.  In  the  back-cross  cultures  half  of  the  flies  were  not-black,  and 
the  not-black  pinkish  flies  were  seen  to  be  less  markedly  "pinkish" 
in  eye-color  than  the  blacks.  In  the  absence  of  black  the  eye-color 
was  more  nearly  like  that  of  the  other  creams,  though  the  amount  of 
dilution  is  less  than  in  any  of  the  other  creams.     In  the  first  two  of 

Table  95. — Offspring  given  by  the  Fi  eosin-eyed  daughters  from  the  out-cross 
of  black  pinkish  females  to  eosin  males,  when  back-crossed  to  black 
pinkish  males. 


Sept.  13.  1914. 

Non-cross-overs. 

Cross-overs. 

Black 
pinkish. 

(Eosin) . 

(Eosin) 
black. 

Pinkish. 

525 

70 
36 
25 

24 

28 

81 
29 
21 
27 
24 

71 
32 
24 
29 
14 

24 
22 
35 
31 
29 

526 

2424 

2425 

2426 

Total .... 

183 

182 

170 

201 

these  back-cross  cultures  (table  95)  males  and  females  were  classified 
together.  Some  question  having  been  raised  in  regard  to  the  accu- 
racy of  the  separation  of  pinkish  from  eosin  among  females,  the 
cross  was  repeated  and  the  readily  classifiable  males  (last  three  cul- 
tures) gave  the  same  result  as  before.  It  was  seen  that  the  new  or 
cross-over  combinations  were  as  numerous  (5 1.4  per  cent)  as  the  original 
classes,  and  this  independent  inheritance  was  taken  to  mean  that  the 
gene  for  pinkish  is  not  in  the  second  chromosome.  While  this  was  a 
mistaken  notion — the  true  relation  being  that  the  gene  is  so  far  away 
from  black  that  in  the  female  there  is  entirely  free  crossing-over — yet 
it  led  to  the  device  of  the  efficient  "double-mating"  method  of 
ridding  a  given  stock  of  an  undesired  recessive. 

THE  DOUBLE-MATING  METHOD. 

If  pinkish  were  in  the  third  chromosome,  then  the  presence  of  the 
black  in  the  pinkish  stock  could  be  of  no  advantage,  and  might  be  a 
very  serious  handicap,  since  it  would  prevent  the  use  of  all  our  third- 
chromosome  stocks  containing  ebony  or  sooty.     The  first  step  in  the 


OF   MUTANT   CHARACTERS. 


249 


elimination  of  black  was  to  mate  together  some  of  the  not-hlack 
pinkish  flies  of  table  95.  One-third  of  the  not-black  ()fTsj)rinK  of  .siu-h 
pairs  should  be  of  the  desired  kind— that  is,  entirely  free  fruni  bhick. 
Our  task  was  then  to  pick  out  from  the  mixture  of  pure  grays  and 
grays  heterozygous  for  black  some  pure  gray  males.  In  this  si)cciiil 
case  we  were  aided  by  the  fact  that  black  happens  to  be  slightly 
dominant— that  is,  the  heterozygous  blacks  are  somewhat  darker  tlian 
the  pure  grays.  While  this  difference  is  not  marked  enough  to  Ije 
used  regularly  in  classification,  it  enables  us  to  pick  out  by  insj)e('ti()n 
a  greater  proportion  of  pure  grays  than  we  would  get  by  random 
selection.  Four  such  males  were  selected  as  being  probaijly  free  from 
black  and  were  mated  to  eosin  females.  Into  the  same  b(jttle  with 
each  pair  of  these  flies  was  put  a  ^'irgin  (red-eyed)  black  female. 
The  offspring  from  these  two  mothers  are  easily  distinguished,  since 
they  are  eosin-eyed  if  from  the  eosin  mother  and  red-eyed  if  from  the 
black  mother.  The  offspring  from  the  black  mother  constitute  a  test 
of  whether  the  father  were  free  from  black,  for  in  this  case  none  of 
the  red-ej-ed  offspring  hatching  in  the  double-mating  culture  should 
be  black,  while  if  the  father  were  heterozygous  for  black  half  of  the 
red-eyed  offspring  should  be  black.  Only  one  of  the  four  cultures  gave 
black  offspring,  and  this  culture  was  then  discarded.  .  .  ,  The  eosin- 
eyed  flies  of  the  other  three  cultures  were  all  heterozygous  for  j^inkish, 
and  at  the  same  time  free  from  black.  By  mating  together  some  of 
these  eosin-eyed  flies  pure  pinkish  offspring  should  be  obtained  as  a 
quarter  of  the  offspring.  A  more  efficient  method,  and  the  one  actually 
followed,  was  to  save  the  fathers  and  mate  them  to  their  eosin-eyed 
daughters,  since  in  this  case  half,  rather  than  a  quarter,  of  the  progeny 
should  be  pure  pinkish. 

Table  96. — B.  C.  offspring  given  by  the  Fi  eosin  star  dichcete  sons,  from  the 
out-cross  of  a  pinkish  female  to  a  star  dichcete  male,  luhen  back-crossed  to 
pinkish  females. 


Aug.  25,  1916. 

Xon-cross-overs. 

Cross-overs  (in  the  male). 

(Eosin) 
star. 

(Eosin) 

star 
dichsete. 

Pinkish. 

Pinkish 
dicha?te. 

Star 
pinkish. 

Star 
pinkish 
dicha'te. 

(Eosin). 

(Eosin) 
dichajte. 

Total 

10 
17 
22 
20 

12 
13 
20 
20 

10 
16 
18 
21 

9 
22 
21 
26 

0 
0 
0 
0 

0 
0 
0 
0 

0 
0 
0 
0 

0 
0 
0 
0 

69 

65 

65 

78 

0 

0 

0 

0 

In  order  to  show  by  an  actual  test  that  the  gene  for  pinkish  is  in  the 
third  chromosome,  it  was  decided  to  take  advantage  of  the  fact  of  no 
crossing-over  in  the  male  and  to  run  a  back-cross  test  of  a  male  hetero- 
zygous for  pinkish  and  for  the  dominant  third-chromosome  cliaracter 


250 


THE    SECOND-CHROMOSOME    GROUP 


dichsete.  It  was  now  realized  that  the  back-cross  tests  of  females 
heterozygous  for  pinkish  and  black  had  not  excluded  the  possibility 
of  pinkish  being  in  the  second  chromosome,  though  they  had  shown 
that,  if  so,  it  could  be  only  in  one  or  the  other  end-region  and  not  near 
black.  Accordingly,  exactly  the  same  procedure  was  followed  as  in 
the  tests  for  the  location  of  cream  b,  that  is,  a  pinkish  female  was  out- 
crossed  to  a  male  which  had  the  second-chromosome  dominant  star 
as  well  as  dichsete.  The  Fi  eosin  star  dichsete  males  were  then  back- 
crossed  to  pinkish  females.  The  result  showed  (table  96)  that  the 
gene  for  pinkish  is  in  the  second  and  not  the  third  chromosome;  for, 
as  well  as  could  be  judged,  none  of  the  star  flies  were  pinkish,  while 
all  the  not-stars  seemed  to  be  pinkish,  and  also  dichsete  was  present 
in  half  of  both  the  star  and  the  pinkish  classes. 

Table  97. — B.  C.  offspring  given  hy  a  star  female  from 
table  96,  when  back-crossed  to  a  pinkish  male. 


Sept.  23,  1916. 

Non-cross-overs. 

Cross-overs. 

(Eosin) 
star. 

Pinkish. 

Star 
pinkish. 

(Eosin.) 

^267{J:::::: 

Total .... 

19 
26 

30 
26 

19 
19 

20 
16 

45 

56 

38 

36 

Table  98. — F'z  offspring  given  by  the  Fi  mid-type  females  and  Fi 
eosin  males,  from  out-cross  of  pinkish  females  to  wild  males. 


Oct.  28,  1916. 

Wild- 
type. 

(Not-eosin) 
pinkish? 

Eosin. 

Pinkish. 

5678 

121 
52 
63 
57 

80 

5 
2 
14 
6 
3 

76 
46 
59 
52 
67 

24 
17 

18 
26 
18 

5680 

5703 

5704 

5705 

Total .... 

373 

30 

300 

103 

LOCUS  OF  PINKISH. 

In  the  light  of  this  test,  and  from  the  fact  that  there  was  about  50 
per  cent  of  crossing-over  between  black  and  pinkish,  we  could  place 
pinkish  in  either  the  extreme  left  or  the  extreme  right  end-region  of 
the  second  chromosome.  Fortunately,  one  advantage  of  the  test  just 
described  is  that  it  left  us  in  possession  of  females  heterozygous  for 
star  and  for  pinkish,  and  a  back-cross  test  showed  (table  97)  that 
there  is  very  free  crossing-over  between  star  and  pinkish.  Pinkish 
is  known,  therefore,  to  be  in  the  right-hand  end  of  the  second  chromo- 
some, in  the  neighborhood  of  arc,  speck,  balloon,  etc.  Had  the  test 
given  almost  no  crossing-over  between  star  and  pinkish,  we  should 


OF    MUTANT    CHARACTERS. 


2'A 


have  known  that  the  gene  for  pinkish  was  in  the  left  end,  but  this  was 
not  the  case. 

A  test  as  to  whether  the  pinkish  gene  would  have  any  visible  effect 
in  the  absence  of  eosin  showed  (table  98)  that  in  a  ven-  small  per  cent- 
age  of  the  flies  homozygous  for  pinkish  there  is  a  very  slight  dilution. 
This  dilution  is,  however,  so  slight  that  rarely  could  one  be  sure  that 
the  effect  observed  is  due  to  dilution  rather  than  to  the  slight  normal 
fluctuation  of  the  red. 

PLEXUS  (p,). 

(Text-fig.  80.) 

ORIGIN  OF  PLEXUS. 

The  venation  character  "plexus"  was  found  by  Bridges  in  a  stock 
culture  of  the  third-chromosome  recessive  spread  wings  (August  20, 
1914,  culture  557).  Fully  10  per  cent  of  the  spread  flies  showed  the 
plexus  venation. 

DESCRIPTION  OF  PLEXUS. 

The  most  striking  feature  of  plexus  is  a  rather  tangled  knot  of  extra 
veins  near  the  distal  end  of  the  fifth  longitudinal  vein  and  the  posterior 
cross-vein,  and  another 
such  knot  near  the  distal 
end  of  the  fourth  longi- 
tudinal vein,  with  an  extra 
vein  running  near  the  mar- 
gins of  the  wing  and  con- 
necting the  two  (see  text- 
figure  80).  Several  other 
small  sections  of  extra  vein 
are  often  present  in  various 
parts  of  the  wing,  most  of 
them  lying  free  in  the  cells, 
but  some  being  branches 
of  or  connected  to  the 
regular  veins.  These  veins 
are  all  sharp  and  clear, 
without  indefiniteness  and 
discoloration  such  as  char- 
acterize the  extra  veins  of 
balloon.  There  is  a  very 
characteristic  bend  forward 
in  the  fourth  longitudinal  vein  before  it  reaches  the  marginal  vein. 

In  less  extreme  individuals  the  connecting  vein  may  be  quite  absent 
and  the  knots  much  reduced.  The  branch  from  the  posterior  cros.'^- 
vein  running  parallel  to  the  fifth  longitudinal  vein  and  also  the  bend 
in  the  fourth  vein  are  the  most  persistent  of  all  the  cliaracters. 


Text-kigure  80. — Plexus  venation. 


252 


THE    SECOND-CHROMOSOME    GROUP 


INHERITANCE  AND  CHROMOSOME  OF  PLEXUS. 

One  of  the  plexus  spread  males  was  out-crossed  to  a  black  female 
and  produced  in  Fi  only  wild-type  flies,  showdng  that  the  character 
was  recessive.  Several  r2  cultures  were  raised  from  pairs  of  the  Fi 
flies,  and  in  these  plexus  reappeared  as  about  a  quarter  of  the  F2  indi- 
viduals. The  plexus  venation  was  present  equally  among  the  F2 
females  and  males,  from  which  it  was  known  not  to  be  sex-linked. 
Likewise  plexus  was  known  not  to  be  third-chromosome  from  the  free 
recombination  of  plexus  and  spread  among  the  F2  individuals.  This 
distribution  of  plexus  and  spread  might  have  been  thought  due  to 
very  free  crossing-over  between  spread  and  plexus  instead  of  the 
random  assortment,  were  it  not  that  the  black  and  plexus  appeared 
in  the  typical  2:1:1:0  ratio,  which  showed  that  the  locus  of  plexus 
is  in  the  second  chromosome. 

From  the  F2  cultures  black  and  plexus  flies  were  crossed  to  each 
other,  with  the  two-fold  purpose  of  obtaining  the  double-recessive  form 
and  of  elimination  the  third-chromosome  recessive  spread. 

LOCUS  OF  PLEXUS. 

The  double  recessive  black  plexus  was  easily  obtained,  and  a  back- 
cross  test  was  made  of  the  amount  of  crossing-over  in  the  female 
between  these  two  loci  (table  99).  The  back-cross  cultures  furnished 
1,026  flies,  of  which  417  or  40.6  per  cent  were  cross-overs.  This  very 
free  crossing-over  located  plexus  in  the  region  of  arc,  if  its  locus  were 
to  the  right  of  black,  or  at  a  point  even  farther  to  the  left  than  streak 
if  it  were  to  the  left  of  black. 

Table  99. — Pi,  black  plexus   9    X  wild  cf ;  B.  C,  Fx  wild- 
type   9    X  black  plexus  cf . 


Jan.  1,  1915. 

Black 
plexus. 

Wild- 
type. 

Black. 

Plexus. 

1084 

1085 

107 

58 

100 

48 

84 

58 

111 

43 

68 
47 
62 
45 

42 
51 
59 
43 

1086 

1099 

Total.... 

313 

296 

222 

195 

A  means  of  easily  testing  these  alternatives  was  soon  afforded  by  the 
discovery  and  location  of  "star,"  which  proved  to  be  a  dominant 
mutation  whose  locus  is  some  distance  to  the  left  of  streak.  A  star 
black  plexus  back-cross  was  made  by  testing  the  Fi  star  daughter,  from 
the  mating  of  a  star  female  by  a  black  plexus  male,  to  black  plexus 
males  (table  100).  Four  such  pair  cultures  gave  1,352  offspring,  of 
which  233  were  double  cross-overs,  343  simple  cross-overs  between 
black  and  plexus,  289  single  cross-overs  between  star  and  black,  and 
487  were  non-cross-overs.     Plexus  gave  42.6  per  cent  of  total  observed 


OF    MUTANT    CHARACTERS. 


253 


crossing-over  with  black  and  46.7  per  cent  with  star,  from  which  it 
was  known  that  the  locus  of  plexus  is  to  the  right  of  bhick.  A  com- 
parison of  the  combined  black  plexus  cross-over  value  of  41.8  with 
other  values  involving  black  indicated  that  the  locus  of  plexus  wa^ 
closest  to  arc,  but  probably  not  quite  as  far  to  the  right,  since  black  and 
arc  gave  42.6  per  cent  of  observed  crossing-over. 

Table  100.— Pi,  black  plexus  cT   X  star   9 ;  B.  C,  F, 
star   9  X  black  plexus  d^ . 


July  20,  1915. 

S' 

S'    1 

b           Px 

S'             1       P, 

S'     1    M 

f>           Px 

1 

b    1 

i        1      Px 

Star. 

Black 
plexus. 

Star 
black 
plexus. 

Wild- 
type. 

Star 
plexus. 

Black. 

SUr 
black. 

Plexua. 

1921 

81 
65 
57 
72 

81 
41 
52 
38 

42 

24 
35 
22 

48 
42 
39 
37 

43 
45 
42 
36 

52 
42 

40 
43 

32 
36 
29 
23 

21 

28 
43 
21 

1922 

1923 

1924 

Total .... 

275 

212 

123 

166 

166 

177 

120 

113 

The  loci  of  plexus  and  arc  were  found  to  be  so  close  together  that  it 
was  too  hard  a  task  to  obtain  the  plexus  arc  double  forms  by  any 
simple  method.     The  plexus  speck  double  was  obtained  fairly  easily. 

Table  101. — Summary  of  all  crossing-over  data  on  plexus. 


Loci. 


Star  plexus. . . 
Squat  plexus . 

Black  plexus  . 


Purple  plexus, 
Plexus  speck.. 


Total. 

Cross- 
overs. 

Per 

cent. 

1,352 

632 

46.7 

82 

39 

47.6 

1,026 

417 

40.6 

1,352 

576 

42.6 

82 

38 

46.4 

2,460 

1,031 

41.9 

344 

164 

47.7 

327 

29 

8.9 

Date. 


July  20,  1915 
AprU  3,  1916 

Jan.     1, 1915 
July  20,  1915 

Apr.    3,  1916 

Feb.  29, 1916 
Feb. 29. 1916 


By- 


Bridges 
Do. 

Do. 
Do. 

Do. 

Do. 
Do. 


Reference. 


PX' 


So', 


S' 


b  Px 


B.  C;  1921-24. 


b      Px 


B.  C;  4044. 


Px-  b  PxB.  C:  1084-'99. 

S' 


Vx\ 


Sq\ 


b  Px 


B.  C;  1921-24 


h     Px 


B.C.;  4044. 


Ula:  Pt  Px  «p  Fi:  S-'iaS-'SS. 
II la;  Pr  Px  »p  Fj;  3535-'53. 


Only  one  linkage  experiment  involving  the  plexus  speck  cross-over 
value  is  available,  and  this  gave  8.9  per  cent  of  crossing-over  (table 
135).  The  locus  of  plexus  is  therefore  about  3  units  to  the  left  of  arc, 
since  arc  gave  5.9  per  cent  of  crossing-over  with  speck. 

This  position  makes  plexus  of  great  importance,  since  it  can  serve 
as  a  new  base  of  reference  for  speck  itself.  At  present  speck  is  located 
by  reference  to  curved,  which  is  too  remote  to  give  an  accurate  measure 


254 


THE    SECOND-CHROMOSOME    GROUP 


of  the  interval,  especially  since  the  amount  of  double  crossing-over 
and  of  coincidence  in  this  region  are  known  only,  by  inference  from 
other  experiments,  there  being  no  intermediate  locus  by  means  of 
which  direct  calculation  could  be  made.  Arc  could  be  used  for  this 
purpose,  but  is  unsuitable  because  of  a  probable  confusion  in  classi- 
fication with  curved.  Plexus,  on  the  other  hand,  being  a  venation 
character  only,  can  readily  be  used  with  curved,  and  its  position  is 
more  favorable  than  arc,  since  it  more  nearly  divides  the  gap. 

Preparations  were  made  to  make  an  extensive  experiment  which 
should  give  data  on  the  plexus  speck  distance  as  well  as  on  several 
others  throughout  the  length  of  the  chromosome.  But  as  yet  this 
has  not  proceeded  further  than  the  synthesis  of  the  multiple  recessive 
needed  (d  b  Pr  c  p^  Sp),  and  of  the  two  parent  stocks  necessary  for  an 
"alternated"  experiment  (S'  b  c  Sp  and  d  Pr  p^). 

A  summarj'-  of  the  crossing-over  data  imvolving  plexus  is  given  in 
table  101.  The  locus  of  plexus  is  about  8.9  units  to  the  left  of  speck, 
or  at  96.2. 

VALUATION  OF  PLEXUS. 

Sturtevant  has  reported  trouble  in  the  classification  of  plexus  in 
certain  crosses,  and  it  is  not  certain  that  all  the  plexus  individuals  can 
be  separated  from  wild-type  where  the  variation  is  great.  In  none  of 
the  experiments  here  reported  was  difficulty  encountered. 

LIMITED. 

(Fig.  81.) 

In  carrying  out  the  black  arc  morula  back-crosses  (culture  513, 
September  13,  1914),  Bridges  noticed  that  there  was  present  a  charac- 
ter somewhat  similar  to  abnormal  abdomen, 
except  that  its  main  effect  was  evident  on  the 
ventral  surface  of  the  abdomen  and  to  a  slight 
extent  on  the  side.  The  chitinous  ventral  plates 
on  the  abdomen,  instead  of  being  full  size  with 
rounded  edges  and  many  regularly  arranged 
small  hairs  (as  in  fig.  81),  were  reduced  often  to 
half  the  size  by  an  irregular  erosion  of  the  edges. 

The  color  also  was  etched.  The  hairs  were  very 
few  in  number,  and  those  irregularly  arranged 
and  directed.  The  dorsal  plates  where  they 
bent  around  to  the  ventral  side  were  affected  in 
the  same  manner  at  their  ends,  though  not  so   Text-figure  si.— Limited 

strikinfflv  bands  to  the  abdomen. 

This  character  was  almost  entirely  limited  to  the  morula  flies  and 
was  distributed  in  such  a  way  that  its  locus  was  certainly  second- 
chromosome  and  probably  to  the  right  of  morula,  though  the  counts 
were  not  made  carefully  enough  to  be  sure  of  this. 


OF   MUTANT    CHARACTERS. 


255 


The  black  arc  morula  stock  was  found  to  be  showing  tiie  limited 
band  character  in  all  or  nearly  all  of  the  morula  fli(>s,  and  this  condition 
has  been  maintained  for  some  five  years,  which  means  tliat  the  linkage 
is  very  close.  It  is  in  fact  not  entirely  certain  that  limited  may  not 
be  found  to  be  still  another  effect  of  morula  itself. 

CONFLUENT  (Q). 
ORIGIN  OF  CONFLUENT. 

In  culture  550  (which  was  part  of  the  tests  of  the  method  of  trans- 
mission of  the  ability  to  produce  exceptions  by  non-disjunction), 
Bridges  found  a  single  male  which  had  thickened,  knotted  veins 
in  the  wing  (September  23,  1914).  The  vein  most  thickened  was 
the  second  longitudinal  opposite  the  anterior  cross-vein,  but  especially 
at  the  tip,  where  it  was  confluent  for  quite  a  space  with  the  marginal 
vein.  In  addition  both  cross-veins  were  thickened  and  irregular. 
The  wing  as  a  whole  was  slightly  smaller  than  usual  and  the  fly 
seemed  rather  sluggish. 

INHERITANCE  OF  CONFLUENT. 

This  male  was  out-crossed  to  a  wild  female  and  in  Fi  i)roduced 
nearly  half  of  the  offspring  with  confluent  veins  (culture  592,  table 
102).  From  this  Fi  result  confluent  was  known  not  to  be  sex- 
linked,  since  the  characters  appeared  in  half  the  Fi  males  as  well  as 
females,  instead  of  in  none  of  the  males  and  all  of  the  females,  as  it 
would  have  done  had  it  been  a  sex-linked  dominant  (like  bar). 

Table  102. — Confluent  cf  {heterozygous)  X  u-ild  9 . 


Oct.  5,  1914. 

Wild- 
type  9  . 

Wild- 
type  cf . 

Conflu- 
ent 9. 

Conflu- 
ent cT. 

592 

627 

24 
52 
42 
41 
10 

20 
3.3 
41 
.37 
11 

17 
38 
37 
36 
12 

11 
47 
33 
46 
14 

628 

901 

10.38 

Total .... 

169 

142 

140 

151 

Some  of  the  Fi  confluent  males  were  again  out-crossed  to  wild 
females,  and  all  the  cultures  of  similar  character  (ta])le  102)  gave  a 
total  of  600  flies,  of  which  291  or  48.5  per  cent  were  confluent.  Thus 
the  viabihty  of  confluent  is  not  bad,  though  the  sterility  is  very  hi^h. 
Very  many  such  matings  failed,  and  this  was  especially  true  of  the 
confluent  by  confluent  matings. 

The  confluent  by  confluent  matings  gave  consistently  about  two- 
thirds  of  the  flies  confluent  and  one-third  wild-t>T>e.  This  suggested 
that,  like  streak,  confluent  was  lethal  when  homozygous. 


256 


THE    SECOND-CHROMOSOME    GROUP 


The  stock  was  run  by  mass-cultures  of  confluent  by  confluent,  and 
these  also  gave  the  same  percentages  of  confluent.  The  stock  was 
maintained  (with  difficulty)  for  two  years  by  this  method  and  there 
was  no  indication  of  an  increase  in  the  percentage  of  confluent,  though 
no  counts  were  made.  These  facts  prove  that  homozygous  confluents 
either  die,  as  supposed,  or  else  play  only  a  negligible  role  through  steril- 
ity if  they  occasionally  survive. 

Table  103. — Pi,  confluent  cf   X  purple  curved  speck    9 
or  X  sepia  peach  ebony  9  . 


Oct.  23.  1914. 

Wild- 
type  9 . 

Wild- 
type  cf . 

Conflu- 
ent 9. 

Conflu- 
ent (f. 

629       

6 
10 

5 
40 

3 
5 

8 
25 

6 

16 

5 

28 

8 
11 

2 
17 

732 

716 

717 

Total 

61 

41 

55 

38 

CHROMOSOME  OF  CONFLUENT. 
Confluent  males  were  out-crossed  to  purple  curved  speck  females  (cul- 
tures 629  and  732,  table  103)  and  to  sepia-peach-ebony  females 
(cultures  716  and  717),  as  Pi  matings  for  male  back-cross  tests  to  deter- 
mine the  linkage  relation  of  confluent  to  the  second  and  to  the  third 
chromosomes  respectively.  The  tests  were  made  with  great  difficulty, 
owing  to  the  sterility  and  low  productivity  of  confluent.  The  second- 
chromosome  tests  gave  a  total  of  71  offspring,  none  of  which  was  a  cross- 
over between  confluent  and  any  of  the  three  second-chromosome  loci 
(table  104).  The  third-chromosome  tests  gave  recombination  between 
confluent  and  the  third-chromosome  loci,  although  as  soon  as  the  results 
of  the  second-chromosome  tests  became  apparent  these  third-chromo- 
some counts  were  discontinued. 

Table  104.— 5.  C,  confluent  Fi  cf  (frojn  table  103)  X 
purple  curved  speck  9 . 


Nov.  26,  1914. 

Conflu- 
ent. 

Purple 
curved 

speck. 

802 

11 
2 
3 
6 

12 

2 

3 

5 

19 

8 

840 

841 

1149 

1150 

Total 

34 

37 

VALUATION  OF  CONFLUENT. 

The  very  low  productivity  and  high  sterility  of  confluent  made  it 
evident  that  there  was  little  use  to  be  obtained  from  the  mutant  in 
spite  of  its  dominance,  good  viabihty,  and  perfect  separability.     The 


OF    MUTANT    CHARACTERS.  257 

determination  of  the  locus  was  not  made,  though  this  would  have  be<'n 
done  had  the  stock  not  died  out  because  of  its  low  i)roductivity  and 
sterility. 

CONFLUENT  VIRILIS. 

Metz  (C.  W.  :Metz,  Journ.  Gen.,  191G,  p.  591)  found  iti  the  species 
Drosophila  virilis  a  mutation  which  was  a  very  striking  count criiart 
of  confluent  of  D.  melanogaster  in  all  respects,  save  that  it  was  neither 
so  sterile  nor  so  non-productive.  The  character  of  the  venation  wa8 
practically  the  same  in  the  two  cases,  though  in  confUiciit  1).  inclm\o- 
gasier  the  venation  nrny  have  been  a  trifle  thicker  and  knottier  in  the 
affected  regions.  Confluent  D.  nn7is  was  a  dominant  which  gave  1  :1 
ratios  upon  inbreeding,  precisely  as  did  confluent  D.  mcUinogasUr. 

There  is  no  doubt  of  the  completely  lethal  effect  of  confluent  ririlis 
when  homozygous,  and  in  confluent  vielanogaster  the  only  indication 
that  an  occasional  homozygote  may  survive  is  the  fact  that  1  out  of  10 
of  the  flies  successfully  tested  by  Metz  gave  a  27  :0  ratio  of  confluent 
to  wild-t^TDe,  instead  of  the  18  : 9  ratio  expected.  The  other  9  flies 
tested  by  Metz  were  all  heterozygous,  as  had  been  all  those  worked 
with  by  Bridges.  It  is  possible  that  this  27:0  ratio  was  the  result  of 
a  balanced  lethal  condition  such  as  obtains  in  truncate,  snub,  beiided, 
and  other  stocks. 

The  fact  that  several  of  the  mutations  secured  in  D.  ririlis  (or  other 
species)  seem  parallel  in  appearance  and  inheritance  with  the  known 
mutants  of  D.  melanogaster  is  of  great  interest  as  an  indication  of  the 
basic  similarity  of  the  two  systems  of  genetic  materials. 

FRINGED  a). 

(Text-figiire  82.) 

ORIGIN  OF  FRINGED. 

In  the  F2  from  a  cross  of  the  sex-linked  wing-character  "jaunty  I" 
to  wild  (culture  1042,  January  20,  1915),  Bridges  found  that  about  a 
quarter  of  the  flies  of  both  sexes  were  showing  an  irregular  distribu- 
tion of  the  hairs  on  the  marginal  vein  of  the  wing.  The  margin  showed 
spots  entirely  denuded  of  hairs  or  with  only  weak  hairs,  while  the 
remaining  hairs  were  frayed  and  irregular  in  directions.  The  wings 
also  were  slightly  smaller,  a  trifle  discolored,  and  occasioniUly  divergent. 

CHROMOSOME  CARRYING  FRINGED. 

I        One  of  the  "fringed"  males  was  out-crossed  to  a  black  female  and 

'    produced  in  F2  the  typical  2:1:1:0  ratio  that  showed  that  the  locus 

of  fringed  is  in  the  second  chromosome  (table  105).     From  the  Fo 

black  and  fringed  inbred  a  stock  of  black  fringed  was  obtained  in  F4. 

A  similar  attempt  to  obtain  a  fringed  speck  double-recessive  stock 

from  the  F2  of  the  cross  of  fringed  by  speck  (table  lOG)  failed  entirely. 


258 


THE    SECOND-CHROMOSOME    GROUP 


LOCUS  OF  FRINGED. 

The  black  fringed  stock,  in  combination  with  the  recently  mapped 
dominant  star,  offered  a  means  of  locating  the  position  of  fringed. 
A  three-locus  back-cross  was  started  by  mating  a  black  fringed  male 
to  a  star  female  and  back-crossing  the  Fi  star  females  by  black  fringed 
males.  The  three  back-cross  cultures  (table  107)  gave  a  total  of  496 
flies,  of  which  153  were  non-cross-overs,  133  single  cross-overs  between 
star  and  black,  141  single  cross-overs  between  black  and  fringed,  and 


Text-figure  82. — Fringed  wing-margin. 

70  were  double  cross-overs.  The  black  fringed  cross-over  value  was 
42.5,  which  places  fringed  at  practically  the  same  locus  as  arc,  which 
gave  42.6  as  the  black  arc  cross-over  value. 

To  determine  the  locus  more  closely  than  this  would  require  fringed- 
speck  or  fringed  arc  back-crosses,  which  have  not  been  made.  The 
only  cross-over  data  on  fringed  are  the  values  calculated  from  the  star 
black  fringed  back-cross  above,  viz,  S'b  =  40.9,  bfr  =  42.5,  8%  =  55.2. 


OF    MUTANT    CHARACTERS. 


259 


In  the  spring  of  1915  Morgan  also  found  fringed,  probaI)ly  through 
use  of  the  same  wild  stock  from  which  it  originally  came  in  the  cro.ss 
to  jaunty  I. 

Table   105.— Pi,  fringed  cf   X  black  9;  Fi  mid-type  9  +  f'l  wild-type  d". 


Feb.  13,  1915. 

Wild- 
type. 

Black. 

Fringed. 

Black 
fringed. 

1361 

216 
150 

UK) 
52 

96 
56 

0 
0 

1362 

Total.... 

366 

152 

152 

0 

Table  106.— Pi,  fringed  cT   X  speck  9;  Pi  wild-type  9   +  Pi  wild-type  cf. 


Feb.  23,  1915. 

Wild- 
type. 

Fringed. 

Speck. 

Fringed 
speck. 

1363 

112 
165 

61 

58 

64 
94 

0 
0 

1364 

Total.... 

277 

119 

158 

0 

Table  107. — Pi,  star  9  X  black  fringed  cf ;  B.  C,  Pi  star  9  X  black  fringed  cf. 


Oct.  23,  1915. 

S' 

S'       1 

b      fr 

.S' 

1        fr 

S'     \    b     \ 

b            fr 

1 

b       1 

1             1       fr 

Star. 

Black 
fringed. 

Star 

black 

fringed. 

Wild- 
type. 

Star 
fringed. 

Black. 

Star 
black. 

Fringed. 

2282 

36 
33 
24 

33 
12 
14 

24 
14 
19 

28 
20 

28 

20 
27 
19 

26 
16 
33 

13 
2 

16 

15 
11 
13 

2283 

2284 

Total 

93 

59 

57 

76 

66 

75 

31 

39 

STAR  (5'). 

(Text-figure  83.) 

ORIGIN  OF  STAR. 

In  an  experiment  by  means  of  which  it  was  proved  that  the  excep- 
tional sons  produced  through  secondary  non-disjunction  are  them- 
selves unable  to  transmit  the  power  of  producing  further  secondary 
exceptions  (Bridges,  1916,  p.  44),  an  eosin  sable  forked  male  was 
found  which  had  an  eye  of  the  moruloid  type  and  which  was  veri- 
similar in  appearance  to  the  sex-linked  mutation  "facet"  (culture, 
1347,  February  12,  1915). 

INHERITANCE  OF  STAR. 

It  was  assumed  that  this  character  was  sex-linked,  since  it  had  ap- 
peared in  a  single  male  in  a  pair  culture,  as  is  usual  with  s<^x-linked 
mutations.     For  this  reason  the  matings  for  Fo  were  made  with(nit 


260' 


THE    SECOND-CHROMOSOME    GROUP 


examining  the  character  of  the  Fi  flies,  and  it  was  not  until  the 
F2  began  to  hatch  that  it  was  reahzed  that  the  other  alternative 
was  correct — that  "star,"  as  the  character  was  called,  was  an  auto- 
somal dominant.  Two  of  the  Fi  pairs  gave  in  F2  no  star  whatever  (1627, 
1629),  while  a  third  pair  (1628,  table  108)  gave  stars  among  both  males 
and  females  to  the  extent  of  half  the  flies  (52  per  cent).  The  fact  that 
half  the  flies  were  stars  showed  that  this  culture 
came  from  a  heterozygous  dominant  and  a  wild- 
type  Fi  pair.  That  star  was  an  autosomal  dom- 
inant was  proved  by  the  sister  cultures  which 
gave  no  stars;  had  star  been  sex-linked  all  the 
Fi  females  would  have  been  star  and  hence  every 
Fo  pair  should  have  given  results  like  those  of 
culture  1628. 

These  facts  were  confirmed  by  the  results  of 
further  tests  of  star  males;  for  star  males  out- 
crossed  to  wild  females  gave  in  Fi  stars  to  the 
extent  of  half  the  flies  (table  109,  337  stars  in  a 
total  of  683,  or  49.3  per  cent),  and  the  stars  were 
evenly  distributed  among  the  males  and  females.  Had  star  been  sex- 
linked,  none  of  the  males  but  all  of  the  females  should  have  been  star. 

Table  108. — Pi,  star  cf  X  wild  9  ;  Fi  pair  (Fi  flies  chosen  at  random). 


Text-figure  83. — Star  eye, 
showing  the  arrangement  of 
the  facets  and  hairs.  Com- 
pare with  the  normal  con- 
dition shown  in  plate  10, 
figure  3c. 


Mar.  12,  1915. 

Wild- 
type  9 . 

Star  9. 

Wild- 
type  cf. 

Star  cf . 

1628 

44 

39 

33 

45 

Table  109.— Pi,  star  d'  X  wild  9 . 


Mar.  27,  1915. 

Wild- 
type  9. 

Wild- 
type  cf . 

Star  9  . 

star  cf. 

1719 

129 

136 

129 

115 

1914 

1915 

28 
27 
26 

24 
32 
37 

1916 

Total .... 

346 

337 

LETHAL  NATURE  OF  THE  HOMOZYGOUS  STAR. 

At  the  same  time  that  the  male  out-crossed  tests  were  made,  a  few 
pairs  of  star  female  by  star  male  were  mated.  In  the  next  generation, 
which  corresponded  to  an  F2,  the  flies  in  one  culture  (1739,  table  110) 
were  exactly  two-thirds  star  and  one-third  wild-type,  which  is  the 
typical  yellow-mouse  ratio  that  had  already  been  met  with  in  Dro- 
sophila  in  the  case  of  streak.  The  other  culture  (1740,  table  110)  gave 
nearer  to  a  3  to  1  ratio.     Further  matings  were  necessary  to  be  sure 


OF    MUTANT    CHARACTERS. 


2G1 


which  ratio  was  really  present.  These  further  ouitures  left  no  doubt 
that  the  ratio  was  really  the  2  :  1  ratio  corresponding  to  a  dorniruint 
lethal  when  homozygous.  The  total  nuniijer  of  stars  in  such  cultures 
was  766,  which  is  67.3  per  cent  of  the  total  nunihor,  wlioro  66.7  per 
cent  are  expected  according  to  the  lethal  assumption. 

Table  110. — Fi  star  9   +  Fj  star  cf . 


Apr.  9,  1915. 

Wild- 
type. 

Star. 

1739 

58 
25 

46 
29 

30 

71 

100 
12 

117 
71 

91 
77 

62 
139 

100 
43 

1740 

1877 

1878 

2025 

2026 

7454 

7455 

Total 

371 

766 

Table  111. — Pi,  star  cf   X  peach  sooty  9 


Mar.  31,  1915. 

Wild- 
type  9- 

Wild- 
type  cf . 

Star  9. 

Star-cf. 

1730 

48 

39 

43 

47 

B  C,  Fi  star  ?  X  peach  sooty  cf . 

Apr.  12,  1915. 

Not-star. 

Star. 

p"         e' 

P"         1 
1 

p' 

P'         1 

1    " 

Peach 
sooty. 

Wild- 
type. 

Peach. 

Sooty. 

Star 
peach 
sooty. 

Star. 

star 
peach. 

St  AT 

Booty. 

1745 

19 
6 

16 
4 
6 

18 

11 
3 

17 
4 

10 

27 

3 
1 
4 
2 
6 
9 

1 
3 
8 
1 
3 
14 

16 
6 

15 
8 
5 

17 

6 
6 

16 
8 
4 

19 

5 

2 
<> 
•) 

3 
10 

5 

2 

4 

3 
o 

5 

1746 

1747 

1748 

1749 

1750 

Total 

69 

72 

25 

30 

67 

59 

24 

21 

The  history  of  the  stock  likewise  proved  the  lethal  nature  of  the 
homozygote;  for  star  flies  were  inbred  for  many  generations  in  iniks.s- 
culture  without  giving  any  closer  an  approach  to  a  pure-breeding  stock. 
Likewise  none  of  the  star  flies  selected  for  out-crossing  on  ver>'  numer- 
ous occasions  ever  proved  to  be  homozygous;  all  gave  the  1  :  1  ratio 
typical  of  a  heterozygous  dominant.  Lately,  much  more  vigorous 
tests  have  conclusively  proved  that  star  is  lethal  when  homoz}-gous. 


262 


THE    SECOND-CHROMOSOME    GROUP 


CHROMOSOME  CARRYING  STAR. 

To  test  the  relation  of  star  to  the  third  chromosome,  a  star  male 
was  out-crossed  to  the  double-recessive  peach  sooty  (peach  is  an  allelo- 
morph of  pink,  and  sooty  an  allelomorph  of  ebony) .  In  Fi  the  flies  were, 
as  expected,  half  stars  and  half  wild- type  (culture  1730,  table  111). 

Some  of  the  Fi  star  females  were  back-crossed  by  peach  sooty  males 
(table  111).  With  two  loci  as  far  apart  as  peach  and  sooty  were  known 
to  be,  there  was  no  need  to  run  a  male  back-cross  test,  since  the  female 
test  must  readily  reveal  linkage  to  one  or  to  the  other  of  these  two 
loci  if  the  tested  gene  is  in  the  third  chromosome.  As  a  matter  of  fact, 
there  was  complete  independence  of  star  and  peach  (52.6  per  cent  of 
recombination)  and  also  of  star  and  sooty  (50,4  per  cent  of  recombi- 
nation). Peach  and  sooty  gave  27.3  per  cent  of  crossing-over,  which  is 
a  trifle  higher  than  the  usual  value. 

LOCUS  OF  STAR. 

Since  the  locus  of  star  was  proved  not  to  be  in  the  third  chromosome, 
the  chances  were  about  50  to  1  that  its  locus  was  in  the  second  chro- 
mosome. This  probability  was  so  great  that  an  extensive  experiment 
was  planned  and  started  without  the  relation  to  the  second  chromosome 
having  been  previously  tested.     This  experiment  was  the  quadruple 

Table  112. — Pi,  star    9   X   purple  curved  speck  cf. 


June  28,  1915. 

Star 
speck. 

Wild- 
type. 

Star. 

Speck. 

1806 

45 
42 

51 

47 

40 
43 

50 
51 

1807 

Total .... 
1808 

87 

98 
83 

83 
95 

101 

back-cross  of  star  and  purple  curved  speck,  which  was  to  serve  several 
purposes.  In  the  first  place,  it  was  to  give  an  accurate  measure  of  the 
amount  of  crossing-over  between  curved  and  speck,  which  was  very 
important,  since  up  to  that  time  only  a  relatively  small  amount  of 
data  was  available  on  this  value  whereby  the  locus  of  speck  and  with 
it  the  entire  right  end  of  the  chromosome  was  mapped  in  relation  to  the 
rest;  in  the  second  place,  it  was  to  establish  the  locus  of  star,  which, 
as  was  then  realized,  might  prove  to  be  the  most  useful  of  all  the  second- 
chromosome  characters.  These  linkage  values  were  both  to  be  con- 
trolled and  linked  up  by  means  of  the  accurately  mapped  loci  purple 
and  curved.  The  third  purpose  was  to  test  more  thoroughly  the  extent 
and  nature  of  the  change  of  crossing-over  Mdth  age  in  different  broods 
and  in  different  regions  of  the  second  chromosome,  but  more  especially 
the  relation  between  this  change  and  the  change  in  the  amount  of 
coincidence  (see  Bridges,  1915). 


OF   MUTANT   CHARACTERS. 


203 


When  the  Fi  flies  from  the  cross  of  star  by  purple  curved  speck  began 
to  hatch,  a  surprise  was  met  with  in  that  half  of  the  flies  were  speck  in 
two  cultures  (1806,  1807),  but  not  in  the  third  (1808,  table  112).  It 
had  not  been  noticed  before  tliat  there  was  any  speck  in  the  star  stock; 
and  it  is  not  clear  how  speck  came  to  be  there,  since  nf)  cross  to  speck 
had  been  made,  and  so  far  as  known  none  of  the  stocks  concerned  in 
the  history  of  star  had  contained  speck  even  as  an  impurity.  However, 
this  circumstance  gave  an  immediate  test  of  the  linkage  reliition  of 
star  and  speck,  since  these  two  cultures  constituted  a  star  speck  back- 
cross  test  of  crossing-over  in  the  female.  The  two  cultures  gave  369 
flies,  of  which  184,  or  49.9  per  cent,  were  cross-overs.  \Vhile  this 
value  is  that  corresponding  to  any  locus  as  far  from  speck  as  black,  or 
any  other  to  the  left  of  black,  it  is  also  the  result  one  would  obtain  if 
star  were  not  in  the  second  chromosome  at  all.  This  possibility 
caused  such  concern  for  the  experiment  already  planned  that  imme- 

Table  113. — Fi,  star  speck  d*  X  purple  curved  speck  9 . 


July  19,  1915. 

Star 
speck. 

Purple 
curved 
speck. 

Star 
curved 
speck. 

Purple 
speck. 

1913 

60 

73 

1 

0 

diately  a  black-cross  test  of  crossing-over  in  the  male  between  star 
and  purple  curved  speck  was  carried  out.  This  male  test  proved  that 
star  is  actually  in  the  second  chromosome,  since  of  the  134  flies  (cul- 
ture 1913,  table  113)  133  were  non-cross-overs,  as  opposed  to  the  very 
free  crossing-over  in  the  female  test. 

CROSSING-OVER  IN  THE  MALE. 

But  one  fly  was  a  cross-over,  since  it  was  distinctly  a  star  curivd 
speck  male,  while  all  other  flies  were  either  star  speck  or  purple  curvet! 
speck.  This  cross-over  fly  occurred  on  the  sixth  day  of  the  counts  of 
a  pair  culture,  so  that  there  is  no  possibility  of  overlap  of  generations; 
and  no  opportunity  for  contamination,  since  no  possibility  of  star 
curved  flies  had  ever  existed  in  any  other  or  previous  culture.  Tliat 
classification  and  pedigree  were  both  as  recorded  was  proved  by  a  t-est 

Table  114. — Cross-over  star  curved  speck  cf   X  purple  curved  speck   9. 


Aug.  7,  1915. 

Star 
curved 
speck. 

Purple 
curved 
speck. 

2048 

26 

29 

made  with  the  cross-over  male.  He  was  out-crossed  to  a  purple 
curved  speck  female  and  produced  star  curved  speck  offspring  in 
equal  numbers  (culture  2048,  table  114).     There  can  be  little  doubt, 


264  THE    SECOND-CHROMOSOME    GROUP 

then,  that  in  this  case  there  had  been  crossing-over  in  the  male  between 
the  loci  purple  and  curved.  It  is  true  that  there  are  two  or  three 
possible  escapes  from  this  necessity.  Thus,  "deficiency"  for  the 
curved  locus  occurring  in  the  star  speck  gamete  of  the  father  would 
give  precisely  this  result.  Like^-ise,  mutation  to  curved  occurring 
in  the  germ-tract  of  the  star  speck  male  would  give  this  result.  "  Du- 
plication" of  the  curved  locus  in  the .  purple  curved  speck  mother 
would  answer  as  well.  All  three  of  these  processes  have  been  met 
with  and  amply  established  elsewhere  in  Drosophila.  (See  especially 
Bridges,  1917,  Genetics,  2,  p.  454.) 

Two  of  these  alternative  explanations,  deficiency  and  duplication, 
were  capable  of  differentiation  from  the  other  two  and  from  each  other 
by  proper  tests,  but  these  were  not  made.  There  was  one  previously 
well-established  case  of  crossing-over  in  the  male  (Muller,  1916),  but 
this  occurred  in  a  very  early  embryonic  stage  and  hence  affected  all 
the  gametes.  It  is  to  be  doubted  if  even  the  case  just  described  is  to 
be  considered  as  brought  about  by  a  mechanism  analogous  to  that  by 
which  crossing-over  in  the  female  is  regularly  effected. 

As  the  first  broods  of  the  star  purple  curved  speck  back-cross  began 
to  hatch  it  became  apparent  that  the  position  of  star  is  very  far  to 
the  left  of  purple — even  further  than  streak.  The  completed  counts 
(table  Ho)  showed  that  star  and  purple  gave  a  total  of  3,010  cross- 
overs in  the  6,766  flies,  or  44.5  per  cent  of  crossing-over.  Streak  had 
given  only  33.1  per  cent  of  crossing-over  with  purple,  so  that  when 
allowance  was  made  for  double  crossing-over,  star  was  calculated  at  a 
position  fully  16  units  to  the  left  of  streak.  With  this  addition  to  the 
total  length  of  the  map  of  the  second  chromosome,  it  was  about  110 
units,  or  very  nearly  twice  as  long  as  the  X-chromosome  map. 

The  crossing-over  between  curved  and  speck  proved  to  be  slightly 
greater  than  the  previous  data  had  indicated,  for  there  was  30.5  per 
cent  of  observed  crossing-over  between  curved  and  speck.  The  total 
available  data  (table  115)  gave  3,037  cross-overs  in  a  total  of  10,042 
flies,  or  30.2  per  cent.  When  a  correction  is  made  for  double  crossing- 
over  according  to  the  probable  coincidence  of  20,  the  locus  of  speck  is 
found  to  be  about  31.6  units  to  the  right  of  curved  or  at  105.1. 

With  respect  to  the  third  problem  involved,  that  of  the  relation  of 
age  to  the  amounts  of  crossing-over  and  of  coincidence,  these  data 
proved  rather  unsuitable,  because  of  the  large  interval  between 
star  and  the  other  three  loci.  Because  of  this  fact  none  of  the  inter- 
\'als  worked  with  were  short  enough  to  exclude  double  crossing-over 
and  furnish  an  uncomplicated  measure  of  the  effects  of  the  age  change. 
This  demerit  was  partly  compensated  by  the  fact  that  nearly  the  entire 
length  of  the  chromosome  was  covered  by  the  four  loci. 

In  general,  these  cultures  and  their  totals  showed  the  usual  drop  in 
the  cross-over  values  of  the  second  broods  (table  116)  and  a  slight 


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THE    SECOND-CHROMOSOME    GROUP 


continued  drop  for  the  third  and  fourth  broods  (table  117).  The  only- 
significant  deviation  from  this  rule  is  in  the  cavse  of  curved  speck,  which 
rose  slightly  in  the  second  broods  (table  118).  This  probably  means 
that  the  normal  fall  was  more  than  compensated  for  by  the  concomi- 
tant change  in  the  amount  of  double  crossing-over  in  this  particular 
region.  The  coincidence  values  for  the  experiment  show  a  very  slight 
drop  with  age,  but  here  again  the  intervals  are  so  long  that  conciseness 
is  lost  and  the  real  effect  on  coincidence  obscured  (table  119). 

Table  118. — Crossing-over  values  for  successive  broods  of  the 
star-purple  curved  speck  back-cross. 


Interval. 

Firsts. 

Seconds. 

Third.s. 

Fourths. 

Star  purple 

Purple  curved . . 
Curve  dspeck. .  . 

44.5 
22.3 
30.5 

41.5 
18.1 
34.6 

40.8 
17.4 
29.8 

37.8 
18.9 
24.1 

Table  119. — Coincidence  values  for  different  regions  of  the 
star  purple  curved  speck  back-cross. 


Regions. 

Firsts. 

Seconds. 

Thirds. 

S'-pr     pr-c. . 
pr-c     c-sp . . . 
S'-pr     c-sp. . 
S'-  pr-c-sp . . . 

102.2 

47.8 

100.3 

41.6 

96.5 

38.7 

104.5 

39.2 

93.5 

39.3 

104.9 

39.0 

Table  120.— Pi,  star  9   X  dachs  d";  B.  C,  Fi  star  9 
X  dachs  cf  from  stock. 


Sept.  15,  1915. 

Star. 

Dachs. 

Star 
dachs. 

Wild- 
type. 

Total. 

2146 

90 
49 
76 
66 
43 
67 
36 
63 
84 
82 

47 
64 
60 
61 
18 
74 
31 
55 
51 
75 

17 
18 
19 
20 
5 
23 
17 
17 
15 
35 

24 
15 
20 
29 
7 
33 
21 
20 
29 
41 

178 
146 
175 
176 
73 
197 
105 
155 
179 
233 

2147 

2148 

2149 

2150 

2218 

2219 

2220 

2221 

2305 

Total 

656 

536 

186 

239 

1,617 

The  star  purple  curved  speck  back-cross  did  not  allow  of  a  close 
calculation  of  the  locus  of  star  because  of  the  great  distance  between 
star  and  purple,  with  little  knowledge  of  the  amount  of  coincidence 
involved.  For  this  reason  it  was  sought  to  use  dachs  as  the  base  of 
reference  for  star,  since  dachs  is  about  23.5  units  nearer  star  than 
purple  is.     Streak  was  known  to  be  even  nearer,  but  the  classification 


OF    MUTANT    CHARACTERS. 


2G9 


of  streak  was  then  in  disfavor  (through  its  failure  in  the  streak  cLichs 
back-cross),  so  that  dachs  seemed  more  practical. 

A  star  dachs  back-cross  furnished  1,()17  flies,  of  which  425,  or  20.3 
per  cent,  were  cross-overs  (table  120).  Several  other  experiments  have 
been  made  which  indirectly  gave  data  on  this  interval.  The  total 
available  data  (table)  furnish  3,472  flies,  of  which  949  or  27.3  per  cent 
were  cross-overs.     When  allowance  for   double   crossing-over   corre- 

Table  121.— Pi,  star  purple  9    X  streak  dachs  d";  B.C.,  F,  .star  streak  9    X 

dach  spurple  cT. 


Aug.  24,  19 IG. 

.S' 

St 

Pr 

S' 

1 

Sk  d 

6"          1   d 

fi 

' 

1       1 

d 

1               Pr 

Sk    1            Pr 

'">'»        d  1    Pr 

Star 
purplo. 

Streak 
dachs. 

Star 
streak 
dachs. 

Purple. 

Star 
dachs. 

Streak 
purple. 

Star. 

Streak 
dachii 
purple. 

4999 

36 
21 
31 
24 
52 
14 
20 
24 
26 
71 

21 
15 
13 
26 
29 
14 
15 
24 
13 
51 

3 
3 
6 

7 
7 
4 
6 
7 
5 
7 

4 
5 

12 
3 

13 
4 
6 

16 
4 

12 

10 
5 

8 

10 

17 
12 
10 

s 

11 

7 

K 

7 

3 
17 

8 
4 
4 

6 
3 
5 
5 
3 
3 
8 

5024 

5025 

4 

5 
9 
3 
4 
6 
2 

10 

5036 

5040 

12 
4 
3 
2 
3 

10 

5041 

5042 

5043 

5055 

5110 

Total 

319 

221 

55 

79 

57 

53 

100 

40 

Aug.  24,  1916. 

S'  1  s, 
1 

b        P» 
d 

S'  1  .St  d  1   Pr 
1              1 

S'           \d\  Pr 

S'  \St\     1 

1             d\pr 

Total. 

St\       1 

Star 
streak 
purple. 

Dachs. 

Star 
streak 
dachs 
purple. 

Wild- 
type. 

Star 
dachs 
purple. 

Streak. 

Star 
streak. 

Dnchs 
purple. 

4999        .    . 

16 

2 
1 

2 

4 

2 

1 
1 

10 

143 
67 

101 
SO 

159 
59 
76 
92 
61 

IhU 

5024 

5025 

5036 

1 

4 

3 
1 

2 

5040 

18 
2 
5 

1 

4 

1 
2 

5041 

1 

5042 .... 

1 

1 
2 

1 

1 
1 

5043 .    . 

5055 

1 

5110 

1 

1 

1 

Total 

1 

46 

» 

Q 

5 

6 

20 

1,027 

sponding  to  the  probable  coincidence  of  30  is  made,  the  locus  of  star 
is  indicated  as  28.8  units  to  the  left  of  dachs  or  4(3.5  units  to  the  left 
of  black. 

As  the  usefulness  of  star  developed,  there  was  greater  necessity  for 
a  still  more  accurate  mapping  of  the  star  locus.  More  recent  work 
with  streak  had  shown  that  tolerably  accurate  results  even  under 


270 


THE    SECOND-CHROMOSOME    GROUP 


unfavorable  conditions  could  be  obtained  with  streak,  especially  as 
long  as  the  calculations  are  restricted  to  the  flies  which  actually  show 
the  streak  character  above  a  certain  definite  grade  of  development. 
A  back-cross  was  therefore  undertaken  between  star  and  streak,  between 
streak  and  dachs,  and  between  dachs  and  purple — all  in  the  same 
experiment.  The  advantage  of  purple  is  that  its  locus  is  securely 
mapped  in  the  main  body  of  loci,  and  its  presence  serves  as  the  con- 

Table  122. — Summary  of  all  cross-over  data  involving  star. 


Loci. 


Star  streak . 

Star  cream  L 
Star  truncate 
Star  dachs. . 


Total. 


396 

389 
549 


Star  black. . 


Star  trefoil . . 
Star  apterous 

Star  purple. 


96 

152 
1,617 

369 

211 

1,027 


3,472 


1,352 

496 

865 
690 

13,104 


Cross- 
overs. 


16,507 


154 
205 


6,766 

1,027 

362 


63 

86 
149 


31 

53 
425 

112 

57 

271 


949 


522 

203 

315 
266 

4,944 


Per 

cent. 


15.9 

22.1 
27.1 


32.3 

34.8 
26.3 

30.4 

27.1 

26.4 


Date. 


27.3 


6,250 


65 

88 


8,155 


3,010 
413 
138 


38.6 

40.9 

36.4 
38.6 

37.7 


37.9 


42.2 

42.8 


3,561 


44.5 
40.2 
38.1 


Aug.  24,  1916 

Oct.  20,  1916 

May  — ,  1917 

Sept.  12, 1915 

Sept.  12, 1915 
Sept.  15,  1915 

Oct.     6, 1915 

Nov.  18,  1915 

Aug.  24,  1916 

Jan.     1, 1915 

Oct.  23,  1915 

Oct.  26,  1915 
Dec.  22, 1915 


By- 


Bridges 

Do. 

Wallace 

Do. 

Do. 
Do. 

Do. 

Do. 

Do. 

Bridges 

Do. 

Do. 
Do. 


Reference. 


S':  ^ — Plb.  C,  Sk  flies  only; 


Crb', 


Std 

S' 


crb 


4999-5110. 
B.C.;  5593+5824. 


Snub;  p.  143,  this  paper. 

dr,  —  F2,  dachs  flies;  2141- 

d  2216. 

idem,  not-dachs  flies. 

S';  —  B.C.;  2146-2305. 
d 


dl; 


dl; 


S' 


dl 


F2;  2217-1659. 


S' 


dl 


B.C.;  2460. 


S';  §L-—2l  B.C.;  4999-5110. 


Std 


Px\ 


S' 


b  Px 


B.C.;  1921-24. 


A; 


S' 


b  fr 

S' 


B.C.;  2282-84. 


43.7 


Dec. 

5, 

1916 

Plough . 

Aug. 
Nov. 

18.' 

1917 
1916 

Morgan 
Bridges 

July, 

11, 

1915 

Do. 

Aug. 

24 

1916 

Do. 

July 

21, 

1917 

Do. 

vgn;     : B.C.;   table  123, 

b  vgu  this  paper. 

di;  ^1A_  B.C.;  2679-7085. 


J.  E.  Z.,  '17,  p.  147;  tempera- 
ture; —  B.C.;  table 7  (22"). 
be 

86(27°),   86(22°).   lll(22°),     173. 


Op;  — 
S';^ 


F2 ;  p.  239,  this  paper. 


Op 


B.C.,  lsts;1836- 

Pr  c  Sp  1894 

S'-— ^B.C;   4999-5110. 

St4 

B.C.,     construction; 
Pr  7391,  7392. 


5';^ 


OF    MUTANT    CHARACTERS.  271 

Table  122. — Summary  of  all  cross-over  data  involving  s/ar— continued. 


Loci. 

Total. 

Cross- 
overs. 

Per 

cent. 

Star  vestigial 

450 

195 

43.3 

Star  curved . 

6,766 

3,164 

46.8 

13,104 

5,959 

44.4 

19,870 

9,123 

46.9 

Star  telescope 

531 

236 

44.4 

Star  plexus. . 

1,352 

632 

46.7 

Star  fringed . 

496 

274 

55.2 

Star  pinkish . 

175 

74 

42.3 

Star  speck. . . 

369 

184 

49.9 

6,766 

3,264 

48.3 

7,135 

3,448 

48.3 

Date. 


Nov.  17,  1915 

July  11.  1915 
Dec.  15.  1915 


May  21.  1916 
July  20.  1915 
Oct.  23.  1915 

Sept.  23,  1916 

June  28,  1915 
July   11.1915 


By- 


Bridges 

Do. 
Plough 


Bridges 
Do. 
Do. 

Do. 

Do. 
Do. 


Rfforence. 


Tgn; 
S';  - 


S' 


B.C.;   laNe  123. 
^  "»"  thia  paper. 

B.C..   lulu:  IS,3<^ 

P^C'P  lstt4. 

J.  E.  Z.;  '17.  p.  147;  teniiMrrft- 

S'' 
tures;  ' —   B.C.;     tabic*    7 

be 
(n").     SK^o).      8.(8").      Ill 
(«").    17,. 

t»;  —  B.C.;4632-'.-J5. 

Px/—- B.C.;  192l-'24. 

6  Px 

S' 

fr;    'B.C. ;  22.82-'84. 

b  fr 

S' 


Pinkish; 


B.C.;  5267. 


pinkish 
S';  S'  sp    B.C.;  lH06-'07. 


firsts;    1836- 

P'  *"  *"  1894. 


necting-link  between  that  body  and  the  other  relatively  poorly  estab- 
lished loci  of  the  experiment. 

There  was  on  hand  a  complex  stock  containing  the  two  genes — 
streak  and  dachs  (provided  by  Muller) — and  this  was  used  in  the  Pi 
mating  to  star  purple,  which  was  made  for  that  purpase.  The  Fi 
star  streak  females  were  back-crossed  to  males  of  a  stock  of  dachs 
purple  which  was  brought  to  production  simultaneously  with  the  Fi 
cultures  (table  121). 

In  making  the  classification  of  the  flies  produced  by  the  quadruple 


back-cross 


.S" 


Pr 


St  d 


the  first  separation  performed  was  that   of 


streak,  disregarding  the  other  characters,  and  including  as  streak  only 
those  quite  obviously  streak.  These  precautions  prevented  the  classi- 
fication of  any  not-streak  flies  among  the  streak,  and  established  a 
uniform  standard  for  streak  among  all  the  various  classes. 

The  separations  were  of  varying  degrees  of  difficulty  in  the  different 
cultures.  The  hardest  were  4999  and  5040,  which  were  fully  iis  diffi- 
cult as  in  the  abandoned  streak  dachs  back-cross.  On  the  other  lumd, 
the  separations  in  culture  5110  were  perfectly  sharp  and  complete. 

The  streak  flies  totaled  396,  and  the  calculation  of  the  cross-over 
values  on  the  basis  of  these  flies  gave  a  star  streak  value  of  15.9  units, 
a  streak  dachs  value  of  16.2,  and  a  streak  purple  value  of  28.S  (table 
121). 


272  THE    SECOND-CHROMOSOME    GROUP 

From  the  first  two  of  these  values  it  appears  that  streak  is  very 
nearly  midway  between  star  and  dachs,  and  that  star  is  about  32.1 
units  to  the  left  of  dachs,  which  agrees  well  with  the  position  as  cal- 
culated from  the  star  dachs  data,  with  allowance  for  double  crossing- 
over.  The  coincidence  for  star  streak  dachs  was  only  9.8,  which  is 
very  low  indeed.  This  means  that  double-crossing  over  in  the  left 
end  of  the  chromosome,  as  we  had  earlier  found  to  be  the  case  in  the 
right  end,  is  very  much  lower  than  it  is  in  the  middle  of  the  chromosome. 
This  would  seem  to  be  connected  in  some  way  with  the  fact  of  median 
attachment  of  the  spindle  fiber,  and  further  analysis  of  the  problem 
should  throw  much  light  on  synapsis  and  crossing-over. 

The  dachs  purple  cross-over  value  of  19.1  is  lower  than  expected, 
and  leads  to  the  mapping  of  dachs  somewhat  nearer  to  black  than 
formerly. 

The  calculation  of  the  other  linkage  values — those  of  which  streak 
is  not  one  of  the  loci  concerned — can  be  made  on  the  total  number  of 
flies  (1,027),  since  these  values  are  established  by  the  classification  of 
fully  separable  characters. 

A  summary  of  all  available  linkage  data  involving  star  is  given  in 

table  122. 

VALUATION  OF  STAR. 

Star  is  now  the  most  used  second-chromosome  mutant.  Its  via- 
bility (heterozygote)  is  on  a  par  with  that  of  the  wild  fly.  Its  position 
is  ideal.  It  interferes  with  the  classification  of  only  one  other  second- 
chromosome  character — morula — which  loses  in  usefulness  because  of 
this  conflict  with  star.  The  separability  of  star  from  the  wild-type  is 
not  as  clear  and  sharp  as  desirable.  There  is  danger  of  overlooking 
some  of  the  star  flies  among  the  wild-type.  This  difficulty  is  not 
general,  but  is  much  more  pronounced  in  certain  cultures,  wherefore 
it  seems  likely  that  most  of  the  suppression  is  due  to  modifiers.  Two 
modifiers  that  markedly  increase  the  separabiUty  of  star  are  known, 
one  of  which  is  in  the  third  chromosome  (the  stock  of  the  double  form  * 
being  known  as  S^)  and  the  other  of  which  is  sex-Unked  (S^  stock). 

There  is  another  danger  in  the  use  of  star  that  must  be  constantly 
guarded  against.  Mutations  of  the  moruloid  type  are  very  frequent 
and  confusion  has  resulted  from  the  presence  of  such  forms  in  experi- 
ments supposed  to  contain  only  star.  When  the  presence  of  such  a 
mimic  is  once  recognized  steps  can  be  taken  to  eliminate  it  and  thereby 
remove  the  difficulty.  One  such,  "pitted,"  apparently  arose  in  the 
star  dichaete  stock,  and  through  the  extensive  use  of  this  stock  be- 
came spread  widely  through  our  experiments  and  other  stocks  derived 
from  these  experiments.  Star  can  therefore  be  used  successfully  only 
by  those  thoroughly  familiar  with  it  and  under  favorable  conditions 
of  illumination  and  magnification,  which  fact  prevents  its  general 
use  by  students. 


OF   MUTANT   CHARACTERS.  273 

The  double  dominant  form,  star  dich^te  (dichn'tc  being  the  most 
important  third-chromosome  mutant),  is  probal)Iy  tlie  most  useful 
single  stock  we  employ.  For  example,  it  has  almost  entirely  suj)- 
planted  the  former  methods  of  testing  the  chromosome  group  of  a 
new  mutant,  and  likewise  furnishes  the  first  test  aj)pliod  in  determin- 
ing loci  within  the  chromosome. 

NICK  M. 

(Text-figure  84.) 

ORIGIN  OF  NICK. 

In  an  experiment  to  determine  the  cause  of  the  linkage  disturl)ance 
found  in  lethal  2  (Morgan  and  Bridges,  1916,  p.  51),  Bridges  found  a 
single  male  which  showed  a  very  slight  nick  or  notch  at  the  tip  of  the 
wing  (culture  2012,  August  7,  1915).  This  nick  cliaracter  would  not 
have  been  noticed  had  not  the  fly  been  very  exceptional  in  another 
regard,  for  he  was  otherwise  wild-type  (though  noted  as  very  dark), 
which  is  a  condition  so  rare  in  the  particular  experiment  that  only  one 
other  wild-type  male  occurred  in  some  thousands  of  offspring.  It  is 
our  custom  to  test  flies  whose  occurrence  is  rare  in  order  to  be  sure  that 
they  are  actually  as  they  appear  to  be,  and  are  not  the  result  of  error 
in  classification  or  parentage.  For  this  reason  the  male  was  out- 
crossed  to  an  eosin  tan  vermilion  female.  In  Fj  all  the  daughters  were 
wild-type,  which  showed  that  no  error  had  been  made  in  cla.ssifying 
the  fly  as  not-tan,  and  tan  was  the  only  character  in  the  parent  experi- 
ment in  which  there  was  any  such  difficulty  in  classification.  The 
sons  were  eosin  tan  vermiliom,  as  expected.  An  Fi  pair  gave  in  Fj 
45  not-nick  and  12  nick  offspring  (culture  2210,  August  28,  1914). 
The  nicks  were  equally  distributed  among  females  and  males,  where- 
fore it  was  know^n  that  the  character  was  not  sex-linked.  The  signif- 
icant feature  of  this  F2  was  that  most  of  the  nick  flies  showed  a 
dark  body-color  like  black,  and  there  were  a  few  other  blacks  thiit 
were  not-nick.  To  test  whether  this  body-color  were  really  black,  a 
"black"  nick  male  was  out-crossed  to  a  bkxck  female  from  stock.  .\I1 
of  the  Fi  flies  were  black.  The  presence  of  black  in  the  F-j  effectively 
disposed  of  the  question  of  the  classification  of  the  rare  fly  in  the  lethal 
experiment — he  was  due  to  contamination  by  some  method  and  Imd  no 
place  in  the  experiment. 

DESCRIPTION  OF  NICK. 

Some  further  tests  were  undertaken  with  the  character  nick,  since 
it  seemed  to  be  a  hitherto  unknown  mutant.  The  niiiin  charact<;ristic 
of  nick  is  the  excision  of  a  piece  of  the  wing-blade  from  the  region  in 
which  the  fourth  longitudinal  vein  meets  the  margin— tliiit  is,  at  the 
tip  and  inner  margin.  This  section  may  be  very  tiny  (fig.  84)  or  more 
extensive   than    in  an  extreme  "notch."     The  more  extreme  nicks 


274 


THE    SECOND-CHROMOSOME    GROUP 


appear  much  like  the  various  types  of  strap,  except  that  the  wings 

do  not  diverge.     There  may  also  be  other  excisions  at  the  outer  edge 

of  the  tip  or  along  either  margin,  rarely  in  the  outer  margin,  often  in 

the  inner. 

CHROMOSOME  CARRYING  NICK. 

One  of  the  black  nick  males  was  out-crossed  to  a  wild  female  and 
two  Fo  pair  cultures  raised.  One  of  these  (2190)  repeated  the  result 
of  the  first  F2,  but  the  other  (2191)  gave  no  nick  whatever.  In  place 
of  nick  there  was  present  vestigial.  Some  of  these  black  vestigial 
flies  were  crossed  to  black  vesti- 
gial flies  of  stock  and  gave  only 
black  vestigial  Fi  offspring.  Others 
mated  together  likewise  gave  only 
black  vestigial  offspring.  The  orig- 
inal male  must,  then,  have  carried 
both  black  and  vestigial  in  one  of 
its  second  chromosomes. 

The  fact  that  most  of  the  F2  nick 
flies  were  also  black  seemed  to 
show  that  black  and  nick  were  in 
the  same  chromosome.  But  that 
this  black-bearing  chromosome  was 
not  the  one  carrying  vestigial 
seemed  no  less  clear  from  the  fact 
that  no  vestigials  had  appeared  in 
the  F2  with  the  black.  This  reason- 
ing leads  to  the  supposition  that 
the  original  male,  noted  as  dark, 
was  really  homozygous  black,  which 

is  not  impossible,  provided  the  weakness  of  the  color  were  due  to 
age  or  that  the  male  had  come  from  a  crowded  or  poorly  fed  culture. 

LOCUS  OF  NICK. 

The  character  nick  had  shown  a  decided  linkage  with  black,  where- 
fore its  gene  was  known  to  be  in  the  second  chromosome.  To  determine 
its  locus  a  back-cross  was  started  by  mating  a  black  nick  male  to  a  star 
female  and  testing  the  Fi  star  females  by  black  nick  males  (table  123). 
Two  of  the  back-cross  cultures  (2327,  2329)  gave  nick;  but  instead  of 
the  nick  being  50  per  cent  of  the  flies  as  expected  from  a  back-cross, 
it  was  only  24.2  per  cent.  Correspondingly  there  was  a  superabun- 
dance of  black  not-nick  flies,  so  that  some  condition  for  the  devel- 
opment of  the  nick  character  was  absent  from  many  of  the  flies.  A 
calculation  based  on  the  nick  flies  showed  that  the  apparent  locus  of 
nick  was  to  the  right  of  black  and  19  units  distant.  This  was  close  to  the 
locus  of  vestigial  and  suggested  that  there  might  be  some  relation 


Text-figure  84. — Vestigial-nick  compound 
showing  a  slight  development  of  the  nick. 
More  extreme  forms  are  scarcely  to  be  dis- 
tinguished superficially  from  "short" 
notches  or  from  broad  straps. 


OF    MUTANT    CHARACTERS. 


275 


between  nick  and  vestigial.  The  possil)ility  of  this  ronneofion  wan 
strengthened  by  the  fact  that  one  other  back-cross  culture  ('2:V2S)  had 
given  black  nick  in  about  the  same  frequency  as  hiui  the  (jthcr  two, 
but  the  remaining  blacks  were  here  vestigkil  instead  of  simply  bhick! 

Table  123.— Pi,  black  nick  d"   X  star  9;  B.C.,  F,  .^^tar  female  X  black  nick 

{black  vestigial   <^   in  case  of  246 L 


Oct.  26,  1915. 

.S" 

S'       1     /,         v,n 

S'              1      Von 

.S'     1   h 

1 

b                 !  gll 

1 

b         1 

1          1      '•» 

Star. 

Black 
nick.^ 

Star 
black 
nick. 

Wild- 
type. 

Star 
nick. 

Black. 

St!ir 
black. 

Nick. 

2327 

14 
75 
31 

57 

60 

7 

39 

9 

32;  19 

58 

2 
11 

8 

21;  18 
35 

4.j 
15 

41 

32 

1 
10 

1 

15;  7 
13 

7 
57 

8 

9 
21 

1 
25 
16 

6 

y 

4 

9;  S 

7 

2329 

2422 

2416 

2461 

The  italicized  numbers  refer  to  vestigial. 

In  the  next  generation,  made  from  star  females  and  black  nick 
males  (from  2329),  there  was  one  culture  giving  black  nicks  and  l)lack8 
(2422),  and  one  giving  black  nicks  and  black  vestigials  (24 IG). 

VESTIGIAL-NICK  COMPOUND. 

It  was  now  realized  that  probably  not  one  of  the  nicks  had  failctl  to 
be  heterozygous  for  vestigial,  and  it  was  suspected  that  the  prescMice 
of  vestigial  might  be  a  necessary  condition  for  the  development  of  the 
nick  character.  It  was  concluded  that  the  mutant  "nick"  might  be 
an  allelomorph  of  vestigial,  which  by  itself  gave  no  visible  difference 
from  the  wild-type  (most  of  the  many  black  not-nicks  being  homozy- 
gous for  the  mutant  gene),  but  which  gave  the  visible  character  "nick " 
when  compounded  with  vestigial 


(-ir) 


The  original  male  was  by  inference  black  vestigial  in  one  second 
chromosome  and  black  nick  in  the  other.  One  of  the  Fi  flics  Imd  car- 
ried the  black  nick  second  chromosome  and  a  wild  second  chromosome, 
while  the  other  carried  the  black  vestigial  second  chromosome  and  a 
wild-type  second  chromosome.  The  Fo  culture  shoukl  then  give  3 
wild-type  flies  to  1  fly  that  would  be  a  vestigial-nick  compound  and 
would  show  the  nick  character. 

The  second  set  of  F2  cultures  gave  one  precisely  like  the  first  and 
one  which  gave  no  nick  whatever,  but  instead  gave  vestigials.  In  tiiis 
case  both  Fi  flies  were  of  the  type  that  received  the  black  \(>siigi;d 
second  chromosome  of  the  black  nick  father. 


276 


THE    SECOND-CHROMOSOME    GROUP 


In  the  back-crosses  the  same  two  kinds  of  Fi    flies  should  occur 

and ),  which  were  both  tested  by  back-crossing 

b    VaU  b     vj         h 


VgU  0  Vg/  5 

with  males  of  the  constitution  t 


VgH 


Table  124. — Pi.  black  nick  cf 


/b_vl\ 
[b      rj 


X  vestigial  cf. 


Nov.  17,  1915. 

Vestigial. 

Wild-type. 

Nick. 

2464 

162 
9P 

56 
50 

85 
56 

2465 

Total 

261 

106 

141 

Feb.  3,  1916. 

9 

cf 

9 

cf 

9 

c^ 

.3095 

c 

31 

7 
35 
35 
42 

1 
40 

6 
30 
42 
35 

"*5 

1 

9 

11 

14 

4 
31 

1 
15 
22 
22 

8 
35 

7 
51 
33 
48 

2 
10 

3 
15 
27 
20 

3096 

3097 

3419 

3420 

3421 

Total 

155 

154 

40 

95 

181 

77 

These  two  types  of  back-crosses  should  be  in  equal  numbers,  and 
3  of  the  first  type  and  2  of  the  second  were  found. 

If  the  above  were  the  true  explanation  of  the  history  of  the  nick 
crosses,   then  whenever  nick  is  out-crossed  to  vestigial  half  of  the 


7/ 

offspring  should  be  vestigial    -  and  half  nick 


This    test    was 


applied  and  found  to  hold  in  part  (table  124,  cultures  2464  and  2465), 
for  while  half  the  flies  were  vestigial  the  remainder  were  not  all  nick 
as  expected,  but  141  were  nick  to  106  that  were  wild-type. 

It  was  assumed  that  not  all  the  compounds  showed  nick  because  of 
overlap,  which  might  well  be  the  case  as  far  as  the  agreement  with 
previous  results  went;  for  the  nicks  had  quite  uniformly  failed  to  be 
as  numerous  as  expected. 

If  the  nick  character  is  the  result  of  a  vestigial-nick  compound,  then 
it  is  more  efficient  in  testing  the  linkage  to  back-cross  by  a  black 

vestigial  male  than  by  a  black  nick  male  ( 9  Xbv  d^  ),  for  in 

\  b     Vg  / 

this  case  twice  as  many  nicks  should  appear,  as  though  the  father  were 
himself  nick.  Several  such  tests  were  started,  but  all  failed  to  breed 
except  one,  which  happened  to  have  come  from  the  black  vestigial 
second  chromosome  of  the  nick  parent  (culture  2461,  table  123). 

A  stock  of  flies  homozygous  for  the  nick  allelomorph  should  be 
obtainable  by  the  paradoxical  method  of  selecting  against  the  nick  as 
well  as  the  vestigial  flies  that  should  appear  on  inbreeding  the  flies 
showing  the  nick  character. 


OF    MUTANT    CHARACTERS. 


2i  i 


The  lines  of  selected  flies  which  show  neither  vestigial  nor  nick  for 
some  generations  should  be  pure  for  the  nick  gene.  Tliis  met  lux  1  was 
somewhat  rough,  but  since  it  offered  a  means  of  carrying  on  the  stock 
without  extra  work  it  was  employed. 


Some  black  nick  males 


ig 


were   crossed    to  vestigial    females 


in  the  course  of  some  later  experiments,  and  these  gave  the  same  sort 
of  result  as  that  noted  in  the  first  division  of  table  124,  except  that 
there  was  found  to  be  a  marked  sex-limited  develoi)ment.  While 
82  per  cent  of  the  vestigial-nick  female  comi)ounds  showed  the  nick 
character,  only  about  half  of  this  percentage  (45  per  cent)  of  the 
males  showed  the  nick  character  (table  124,  last  division).  This  sex- 
limitation  is  in  the  opposite  direction  from  that  previously  known  in 


the  case  of  the  vestigial-antlered  compounds  I  — 


s(^j-),fo 


r  there  most  of 


the  compound  males  showed  the  an  tiered,  while  only  a  few  of  the 
females  were  like  antlered. 

DACHS-LETHAL  (t/,). 

ORIGIN  OF  DACHS-LETHAL. 

The  first  demonstration^  of  a  recessive  autosomal  lethiil  in  Dro- 
sophila  came  through  the  effort  to  determine  more  closely  the  locus 
of  star  by  means  of  its  linkage  relations  to  dachs  (October  6,  1915, 
culture  2217). 

Table  125.— Pi,  star  9   X  dachs  cf ;  Fi  star  9  +  Fi  star  cf . 


Sept.  12.  1915. 

Star. 

Dachs. 

Star 
dachs. 

Wild- 
type. 

2141 

2142 

30 
42 
59 
49 
15 

55 

12 

8 

11 

3 

6 

25 

3 
2 
4 
8 

14 

6 
13 
10 

8 
6 

10 

2143 

2144 

2145 

2216 

Total 

250 

65 

31 

63 

The  back-crosses  which  furnished  the  bulk  of  these  data  have  already 
been  given  in  the  section  on  star;  in  addition  some  F2  cultures  from 
the  cross  of  star  by  dachs  were  raised  by  inbreeding  Fi  star  males  and 
females  (table  125).  It  is  comparatively  rare  that  an  Fo  culture  is 
raised  under  such  circumstances,  since  in  general  the  back-cro.'v';  is  so 
much  more  efficient.  In  this  case  the  Fo's  were  raised  as  an  exiimple 
of  the  lethal  effects  of  homozygous  star  in  combimition  with  the  link- 
age ratios.     Because  of  the  fact  that  all  homozygous  stars  die,  the  Ft 

1  In  the  case  of  the  aberrant  ratios  of  pink,  Liff  (15)  had  suggested  that  an  autooomal  lethal 
might  be  the  explanation. 


278 


THE    SECOND-CHROMOSOME    GROUP 


ratios  are  simplified  more  than  in  the  ordinary  F2.  Thus  in  table  125, 
the  classes  of  star  dachs  and  wild-type  are  both  simple  cross-over 
classes  (x),  the  dachs  are  simple  non-cross-overs  (n),  and  the  star 
class  only  is  complex,  being  a  double  non-cross-over  plus  a  single 
cross-over  {2n-\-x).  In  the  ordinary  coupling  F2,  the  wild-type  class, 
which  corresponds  to  the  star  of  this  experiment,  is  more  complex 
{3n+2x). 

Six  of  the  F2  cultures  gave  the  expected  results,  with  about  33  per 
cent  of  crossing-over  between  star  and  dachs;  the  other  culture  (2217, 
table  126)  gave  no  dachs  whatever  among  116  flies,  one-third  of  which 
were  expected  to  be  dachs. 

Table  126. — Progeny  from  star  males  and  females  heterozygous 

for  dachs  lethal  (  - — 7-  | . 


Oct.  6,  1915. 

Star. 

Dachs. 

Star 
dachs. 

Wild- 
type. 

2217 

93 

68 

104 

68 
65 

42 

15 

69 

102 

23 

11 

13 

6 
11 

6 

3 

16 

23 

2345 

2423 

2592 

2593 

2652 

2653 

2658 

2659 



Total 

2344 

2346 

626 

113 
35 

112 

50 
10 

DACHS-DEFICIENCY? 

The  phenomena  of  ''deficiency"  had  just  been  worked  out  in  detail 
in  the  case  of  forked-bar  deficiency  (Bridges,  1917),  and  accordingly 
the  non-appearance  of  the  dachs  where  both  parents  were  expected 
to  be  heterozygous  was  immediately  attributed  to  the  occurrence  of 
deficiency  for  the  dachs  gene.  It  was  thought  that  the  character  dachs 
was  unable  to  appear  because  of  the  physical  absence  or  the  complete 
inactivation  of  the  dachs  gene.  One  of  the  most  striking  features  of 
forked-bar  deficiency  had  been  the  lethal  nature  of  the  change.  The 
same  process  that  had  removed  the  genes  for  forked  and  bar  and  the 
intermediate  region  had  replaced  their  action  with  a  lethal  agency. 
Immediately  the  supposed  case  of  dachs-deficiency  was  examined  to 
see  whether  in  it  also  the  elimination  of  a  gene  had  resulted  in  the 
substitution  of  a  lethal.  The  ratio  of  23  wild-type  to  93  stars  showed 
unmistakably  that  a  lethal  agency  was  operative;  that  the  seat  of 


OF   MUTANT   CHARACTERS. 


279 


its  activity  was  in  the  chromosome  which  had  contained  dach.s;  and 
further,  that  its  locus,  as  judged  from  the  Hnkagc  with  star,'  wa« 
certainly  very  close  to  that  normally  occupied  by  dachs. 

The  case  for  dachs-deficiency  was  further  strengthened  when,  as  the 
result  of  tests,  a  third  correspondence  to  forked-deficiency  wa«  estab- 
lished. A  female  having  forked-deficiency  in  one  X  and  forked  in  the 
other  is  in  effect  haploid  for  the  forked  gene,  and  accordingly  such  a 
female  shows  the  forked  character  just  as  in  the  male,  which  is  nor- 
mally haploid  for  forked  (and  for  all  other  sex-linked  genes). 

Table  127. — Pi,  star  flies  from  dachs-lethnl  stock  out-crossed  to  dachs. 


Nov.  17.  191.5. 

Star. 

Dachs. 

Star 
('achs. 

Wild- 
type. 

2486...! 
2487.../ 

+  di 

/     74 
I      53 

28 
58 

0 
0 

0 

U 

2460.... 

H' 

88 

66 

16 

41 

2458.... 

H' 

62 

71 

If  a  fly  were  carrying  "dachs-deficiency' '  in  one  second  chromosome 
and  star  in  the  other  and  were  out-crossed  to  dachs,  then  half  the  off- 
spring should  be  dachs,  since  these  flies  should  carry  the  dachs  gene 
in  one  second  chromosome  and  in  the  other  no  normal  gene  to  oppose 
its  action.     When  the  test  was  made  half  of  the  offspring  were  diichs 

and  half  were  not  (table  127).     In  appearance  these  dachs  flies  ( M 

were  indistinguishable  from  the  dachs  flies  of  regular  stock.  The 
dachs  flies  were  distributed  according  to  the  usual  linkage  relations 
of  star  and  dachs.  One  pair  failed  to  give  dachs  offspring  (2458), 
corresponding  to  the  crossing-over  that  occurs  normally  between  star 
and  dachs  whereby  a  certain  proportion  of  the  star  descendents  are  not 
heterozygous  for  the  lethal. 

BALANCED  LETHALS. 

It  was  obvious  that  the  stock  had  to  be  carried  on  as  a  recessive 
autosomal  lethal — that  is,  by  mating  together  two  flies  each  heterozy- 
gous for  the  lethal.     The  most  advantageous  method  of  doing  this 

was  found  to  be  to  use  the  flies  heterozygous  for  star  also  i- — -  j , 

since  in  this  case  advantage  could  be  taken  of  the  fact  that  most  of  the 
flies  which  would  be  homozygous  for  not-lethal  would  at  the  s.'ime  time 
be  homozygous  for  star  and  hence  be  eliminated.  Most  of  the  stars 
in  each  generation  would  continue  to  be   heterozygous  for  the  letlial. 


280  THE    SECOND-CHROMOSOME    GROUP 

Only  those  which  resulted  from  crossing-over  between  star  and  the 
ocus  for  dachs  would  fail  to  carry  the  lethal.  If  these  two  loci  had 
been  closer  together,  then  fewer  such  cross-overs  would  occur  and 
selection  could  be  correspondingly  relaxed.  In  the  case  of  a  pure 
breeding  stock  of  ''beaded,"  Muller  found  that  there  was  an  autosomal 
lethal  in  the  not-beaded  third  chromosome,  and  very  close  indeed  to 
the  locus  of  the  beaded  allelomorph,  so  that  no  selection  at  all  was 
needed.  This  principle,  first  used  consciously  in  carrying  on  the 
stock  of  dachs-lethal,  was  called  by  IMuller  "balanced  lethals"  as 
worked  out  by  him  in  the  analysis  of  the  beaded  stock.  Muller  has 
shown  that  this  principle  has  wide  application,  and  may  solve  some 
of  the  knotty  problems  of  the  genetics  of  Oenothera,  such  as  pure- 
breeding  heterozygotes,  the  continual  production  of  rare  forms  called 
mutants  (which  by  this  principle  are  due  to  crossing-over  rather  than 
to  a  fresh  occurrence  of  the  mutative  process),  and  also  the  appearance 
of  t\Adn  hybrids  from  certain  crosses. 

It  was  quickly  recognized  that  the  dachs-deficiency  explanation  was 
alternative  to  that  of  a  simple  recessive  autosomal  lethal  occurring 
in  a  locus  close  to  that  of  dachs,  the  recessive  dachs  gene  being  present 
and  unchanged,  but  prevented  from  giving  rise  to  the  dachs  character, 
because  all  (or  nearly  all)  of  the  homozygous  dachs  flies  were  also 
homozygous  lethal,  and  hence  never  appeared  as  adults.  All  of  the 
three  parallels  to  forked-deficiency  were  equally  explainable  on  the 
linked  lethal  view.  A  possible  method  of  distinguishing  between  the 
two  conditions  was  offered  by  the  appearance  or  non-appearance  of 
dachs  flies  upon  inbreeding.  If  the  phenomena  were  due  to  dachs- 
deficiency,  then,  of  course,  no  dachs  could  ever  appear,  since  the  lethal 
effect  involved  the  dachs  locus  itself.  But  if  two  separate  and  dis- 
tinct loci  were  involved — dachs  and  a  neighboring  lethal  locus — then 
by  crossing-over  between  them  dachs  should  reappear.  For  this  reason 
a  most  careful  count  was  kept  of  the  early  stock  cultures,  which  were 
run  by  the  method  of  inbreeding.  For  four  generations  this  was 
continued  (table  126)  and  not  a  single  dachs  fly  appeared  among  the 
fhes.  Besides  the  pair  cultures  recorded  in  table  126  (which  were 
necessary  in  order  to  avoid  all  danger  of  losing  the  stock  by  crossing- 
over  between  star  and  the  lethal),  many  other  mass-cultures  were 
raised  for  the  purpose  of  giving  full  opportunity  for  dachs  to  reappear. 
These  were  not  counted,  since  the  composition  of  the  parents  was  of 
two  sorts  and  the  ratios  correspondingly  confused.  Approximately 
5,000  flies  were  examined,  however,  without  finding  any  dachs. 

The  appearance  of  a  dachs  fly  would  have  established  the  linked 
lethal  view;  but  the  non-appearance  of  such  flies  did  not  prove  the 
deficienc}^  view,  but  only  that  if  a  linked  lethal  were  present  its  locus 
was  extraordinarily  close  to  that  of  dachs.  Such  an  appearance  of  a 
dachs  fly  would  be  parallel  to  the  appearance  of  certain  Oenothera 
"mutants,"  according  to  the  application  made  by  Muller. 


OF    MUTANT    CHARACTERS.  281 

There  was  another  possible  method  of  distint:;uishing  between  these 
views,  which  was  tried.  It  had  been  found  that  the  occurrence  of  the 
forked-bar  deficiency  had  distributed  the  Hnkaj^c  relations  in  the  first 
chromosome  in  a  definite  way.  All  crossing-over  in  the  rcf^ion  between 
forked  and  bar  was  eliminated,  as  proved  by  direct  tests  with  forked 
and  bar,  and  likewise  by  tests  of  the  decrease  in  the  amount  of  crossin^;- 
over  from  that  which  nominally  occurs  between  the  nean^st  lori  on 
either  side,  namely,  rudimentary  and  fuseil.  In  the  case  of  dachs- 
lethal  there  was  no  other  gene  known  to  be  included  in  the  deficient 
region  itself,  so  that  direct  tests  were  impossible;  and  even  worse, 
there  were  no  loci  close  enough  to  dachs  to  give  a  meiisure  of  the 
decrease  unless  it  were  very  marked.  It  was  thought  possible  tlrnt 
a  rather  extensive  disturbance  might  be  initiated  by  a  reliitively  short 
deficiency,  since  the  shortened  chromosome  might  well  prevent  perfect 
synapsis  for  a  much  longer  region  because  of  the  "pucker." 

The  only  practical  but  unsatisfactory  test  that  could  be  made  w;is 
through  black,  which  was  the  nearest  workable  locus  to  the  right,  and 
star,  which  was  the  only  locus  to  the  left  that  could  be  used  without 
inaccuracy. 

If  the  dachs  locus  were  deficient  it  could  still  be  controlled  by  means 
of  the  haploid  dachs  flies  produced  by  testing  with  dachs.  Thus  the 
proposed  experiment  involved  a  female  carrying  a  star  dachs-defi- 
cient  second  and  a  black  second  chromosome,  to  be  tested  by  means 
of  a  dachs  black  male.  Star  and  dachs  were  put  in  the  same  chromo- 
some because  that  method  was  far  easier,  and  also  because  the  recip- 

rocal  back-cross  ( ^ cf  X6  9  )  offered  a  means  of  carrying 


on  the  dachs-lethal  stock  with  no  opportunity  for  crossing-over,  since 
the  only  heterozygote  was  the  male,  in  which  sex  no  crossing-over 
occurs.  The  stock  had  been  run  with  star  and  dachs-lethal  in  opposite 
second  chromosomes.    To  get  them  into  the  same  chromosome  a  feiruile 

( j  was  out-crossed  to  a  dachs  male.  The  star  dachs  cross- 
over offspring  contained  a  chromosome  of  the  desired  composition 
(- — -^—j.     To  be  sure  of  retaining    this    chromosome,    and   not 

getting  a  plain  star  dachs  chromosome  by  crossing-over,  a  male  of  this 
type  was  used  in  the  next  step,  which  was  an  out-cross  to  black  (culture 
2613).  All  of  the  star  offspring  of  this  cross  were  of  the  desired  com- 
position (51A_  j .     Stock  was  started  by  mating  such  males  to  black 

females  and  repeating  each  generation  (table  128).  No  sjiecial  pains 
need  be  taken  to  see  that  the  females  are  virgin  in  this  stock,  which  is 
an  advantage  not  possessed  by  the  similar  selecteil  stocks  of  the  sex- 
linked  mutants  where  the  heterozygote  has  to  be  the  female  and  virgin. 


282 


THE    SECOND-CHROMOSOME    GROUP 


The  females  back-crossed  to  dachs  black  males  produced  the  results 
shown  in  table  129  (cultures  2679,  2680,  2681). 

The  crossing-over  between  star  and  dachs  was  found  to  be  normal, 
but  the  crossing-over  between  dachs  and  black  was  the  lowest  ever 
encountered  (outside  recognized  linkage  variations) ,  being  only  11.1 
per  cent,  while  the  mean  calculated  from  6,725  other  flies  was  17.8  per 

S'  di 


Table  128. — Cultures  of  dachs-lethal  stock, 


d'   X  b  9 


Dec.  19,  1915. 

Star. 

Black. 

2655 

55 

12 

1.35 

148 

48 

8 

151 

163 

2656 

2657 

2761 

Total .... 

350 

370 

cent.  This  same  experiment  was  repeated  in  1917  (cultures  7083,  7085, 
table  129)  and  the  same  result  was  obtained,  since  the  crossing-over 
between  dachs  and  black  was  only  10.2  per  cent.  The  lowest  regular  value 
found  for  dachs  black  was  16.7  (found  by  Muller  in  his  progeny  tests.) 
It  would  seem  that  these  values,  which  represent  a  decrease  of  39 
per  cent  from  the  standard  values,  are  sufficiently  aberrant  to  prove 
that  the  case  is  not  to  be  explained  by  a  simple  lethal,  linked  to  dachs. 

Table  129.— Pi,  star  dachs-lethal  9   ( j]X  black  d^;  B.C.,  Fi  star  9 

I — r  I  X    dachs  black   (t)    cf . 


Dec.  22,  1915. 

S' 

di 

b 

S'    1 

b 

S'     di 

1  b 

S'            1 
\    di     \    b 

Total. 

1  di 

1 

star 
dachs. 

Black. 

Star 
black. 

Dach.s. 

Star 
dachs 
black. 

WUd- 
type. 

Star. 

Dachs 
black. 

2679 

37 
67 
29 

34 
20 

29 
81 

48 

52 
22 

13 
36 
16 

20 
12 

16 

28 
21 

28 
6 

5 

8 
7 

5 

4 

9 
15 

7 

8 
2 

109 
236 
129 

148 
68 

2680 

2681 

7083 

1 

1 

1 

1 

1 

7085 

Total 

187 

232 

97 

99 

29 

41 

3 

2 

690 

There  is  a  possible  escape  from  the  conclusion  that  the  case  is  one  of 
dachs-deficiency,  through  the  additional  assumption  of  a  ''cross-over 
gene"  which  will  give  this  specific  disturbance  of  crossing-over. 

Sturtevant  has  found  two,  and  Bridges  one  such  mutation  in  the 
second  chromosome ;  but  none  of  these  gives  a  result  very  closely  com- 


OF   MUTANT    CHARACTERS.  2^3 

parable  to  that  found  here.  It  is,  howover,  possible  that  tho  one 
found  by  Bridges  (C  lis)  may  on  further  investigiition  be  found 
comparable. 

On  the  whole,  the  evidence  is  in  entire  agreement  with  the  assump- 
tion of  dachs-deficiency,  but  at  the  same  time  is  not  in  such  disiigreo- 
ment  with  the  Hnked-lethal  view  as  to  disprove  it.  Hcforo  either 
alternative  can  be  dropped  it  is  necessary  to  repeat  the  two  test« 
which  offer  definite  solution — the  search  for  dachs  flies  from  an  inbred 
line  and  far  more  rigid  tests  of  the  system  of  linkage  tluit  is  present. 
Meanwhile,  the  ambiguous  term  "dachs-letlial"  will  be  retained  to 
cover  both  possibilities.. 

SQUAT  (5,). 

(Text-fig.  85.) 

ORIGIN  OF  SQUAT. 

In  tracing  the  course  of  "high"  non-disjunction  (Bridges,  1910)  a 
female  heterozygous  for  the  sex-hnked  genes  vermilion,  siible,  garnet, 

and  forked  ( —  )  was  tested  for  the  occurrence  and  i:)ercentage  of 

secondary  exceptions  by  out-crossing  to  a  male  from  the  bar  Csex- 
linked  dominant)  stock.  One  of  the  regular  vermilion  forked  sons  of 
this  pair  (culture  No.  2480)  was  found  (November  29,*  1915)  whose 
wings,  legs,  and  body  were  considerably  shorter  than  normal,  gi\ing 
a  *' squat"  appearance  to  the  fly.  Only  one  such  squat  fly  was  found 
among  372  offspring  from  this  pair,  which  in  such  cases  is  always  a 
strong  indication  that  the  mutant  is  either  dominant  or  sex-linked. 

In  order  that  a  non-sex-linked  recessive  should  appear  in  a  culture, 
both  parents  must  be  heterozygous  for  the  gene,  and  in  such  cases  the 
recessive  character  appears  as  a  quarter  of  the  individuals  and  not  as 
a  single  individual,  as  was  here  observed. 

INHERITANCE  OF  SQUAT. 

The  squat  male  was  out-crossed  to  a  wild  female,  and  in  Fj  jiroduced 
(culture  2635)  a  total  of  53  squat  flies  to  47  not-squats.  This  means 
that  the  mutant  is  a  dominant  and  the  original  mide  was  likewise  a 
heterozygous  dominant.  That  it  is  an  autosomal  dominant,  rather 
than  a  sex-linked  dominant,  was  proved  by  the  fact  that  half  (22)  of 
the  Fi  squats  were  males;  had  the  squat  been  sex-linked  none  of  the 
sons  could  have  shown  the  mutant,  since  their  single  X  chromosome 
comes  from  their  mother  and  not  from  their  father. 

A  squat  male  and  female  from  Fi  were  inbred,  and  gave  in  Fo  121 
squats  to  53  not-squats  (No.  2728).  This  seemed  to  be  an  aj^i^roxi- 
mation  of  a  3  :  1  ratio  rather  than  of  a  2  :  1  ratio,  and  was  thought  to 
indicate  that  the  dominant  is  probably  not  lethal  when  homozygous. 


284 


THE    SECOND-CHROMOSOME    GROUP 


Nearly  all  of  our  other  dominant  autosomal  mutants  are  lethal  when 
homozygous,  and  therefore  give  2  :  1  ratios  when  inbred,  as  in  the  type 
case  of  the  yellow  mouse. 

DESCRIPTION  OF  SQUAT. 

The  squat  flies  seen  in  culture  2636,  and  in  subsequent  cultures,  may 
be  more  exactly  described  by  aid  of  the  drawing  of  the  somewhat 
atypical  specimen  of  figure  85.  The  most  striking  change,  and  the  one 
most  dependable  in  classification,  is  that  of  the  wing,  which  is  about 
80  per  cent  the  normal  length,  is  slightly  broader  than  normal,  and  has 
a  blunt  end.  The  whole  wing  is  of  a  somewhat  weaker  texture,  with  a 
tendency  to  droop  like  "arc."  The  color  of  the  wing  is  somewhat 
cloudy  and  brownish  instead  of  the  clear  gray  of  the  normal.  The 
wings  are  also  sometimes  slightly  divergent.  The  thorax  is  short, 
broad,  and  rather 
flattened  on  top. 
The  head  likewise 
is  broad  from  side 
to  side,  and  quite 
often  the  eye  has 
a  protruding  lump 
which  is  caused  by 
an  extra  antenna 
pushing  partly  or 
entirely  through. 
The  legs  are  weak 
and  shortened, 
especially  in  the 
basal  joints.  None 
of  the  above 
changes  are  very 
marked  or  of  uni- 
form occurrence. 
One  learns  to  recog- 
nize the  type  much  as  in  the  case  of  certain  wild  species,  or  Oenothera 
mutants,  by  the  ensemble  of  slight  differences. 

CHROMOSOME  OF  SQUAT. 

To  test  whether  squat  is  third-chromosome  or  not,  squat  males 
were  out-crossed  to  the  third-chromosome  dominant  dichsete.  Both 
Fi  pairs  (2730,  2829)  gave  very  few  squats,  and  these  difficult  of  class- 
ification. It  seemed,  and  this  has  proven  to  be  the  case,  that  the  squat 
character  behaves  as  does  truncate  and  several  other  of  our  mutations. 
Presumably,  like  truncate,  it  owes  most  of  this  evanescence  to  its 
extreme  sensitiveness  to  modification,  both  in  intensification  and  sup- 
pression, brought  about  by  the  action  of  different  combinations  of 


Text-figure  85. — Squat. 


OF    MUTANT    CHARACTERS.  285 

genes.  Such  eclipses  are  only  temporary,  hut  are  serious  in  tliiit  they 
spoil  the  usefulness  of  the  mutation  as  a  working  tool. 

One  of  the  Fi  squat  dichaete  males  was  out-crossed  to  a  wild  fonuilo 
and  produced  four  classes  of  offspring  (culture  2993;  Sg  21  :   D'  20  :  S 
D'  20  :  +24).     Since  this  was  a  back-cross  test  of  the  miUe,  it  is  evident 
that  squat  is  not  in  the  third  chromosome.     If  squat  were  third- 
chromosome  there  would  have  been  no  squat  dicha'tes. 

At  the  time  that  the  dichaete  test  was  made  a  parallel  cross  to  stur  was 
started  to  test  the  relation  of  squat  to  the  second  chromosome.  Here 
also  in  the  Fi  cultures  (2738,  2828)  the  squat  could  be  distingui.^hed 
only  poorly. 

The  back-cross  test  of  the  male  attempted  in  this  case  failed,  prol>- 
ably  through  sterility.  But  the  answer  was  obtained,  though  less 
surely,  by  a  female  test  started  at  the  same  time.     One  of  the  Fi  star 

squat  females  f — —  j,  when  out-crossed  to  a  wild  male  gave  among 

the  offspring  a  few  star  squats  (culture  2827).  Since  the  squat  was 
poor,  no  accurate  records  were  kept,  though  it  seemed  very  probable 
that  squat  was  showing  linkage  to  star.  That  the  eclipse  of  squat  did 
not  mean  extinction  was  proved  in  the  next  generation;  for  a  star 
female  and  a  not-star  male,  both  selected  as  showing  no  squat,  produced 
squat  offspring  (3061).  These  squats  were  dominants,  not  recessives, 
as  proved  by  out-crossing  them  to  wild  flies,  whereupon  in  Fi  neiirly 
half  of  the  flies  were  squats  (3339) . 

OTHER  MUTATIONS. 


In  culture  3061,  just  described,  the  second-chromosome  recessive, 
"narrow"  v^ngs  was  found  (February  7,  1916).  From  the  linkage 
with  star  which  it  showed,  it  had  evidently  been  introduced  to  the  cross 
through  star. 

In  culture  3858,  which  was  simply  a  stock  culture  of  squats  whose 
parents  were  taken  from  3061,  there  reappeared  the  second-chromo- 
some recessive  mutant  "commas,"  which  had  apparently  been  carrried 
along  in  the  same  chromosome  with  squat,  but  being  recessive  had 
hitherto  no  opportunity  to  show  itself. 

LOCUS  OF  SQUAT. 

It  had  by  now  become  apparent  that  squat  was  second-chromosome, 
and  it  was  thought  advisable  to  make  a  rough  determination  of  its 
locus.  Squat  was  therefore  crossed  to  black  i^lexus  and  a  back-cross 
test  of  the  female  made.  Black  is  a  control  for  the  middle  and  plexus  for 
the  right  end  of  the  second  chromosome.  No  control  of  the  left  end 
was  made,  since  the  fairly  free  crossing-over  between  star  and  scjuat 
observed  in  some  stock  cultures  had  made  it  evident  that  the  locus  of 
squat  is  fairly  distant  from  the  left  end  of  the  chromosome. 


286 


THE    SECOND-CHROMOSOME    GROUP 


The  one  back-cross  culture  that  produced  results  (4044,  table  130) 
showed  that  squat  is  not  far  from  black,  there  being  9  cross-overs  in  a 
total  of  82  flies,  or  11.0  per  cent. 

The  pair  of  complementary  classes  with  the  smallest  sum  is  squat 
black  and  plexus,  which  are  therefore  probably  the  double  cross-overs. 
If  this  is  true,  then  squat  lies  to  the  left  of  black,  a  position  which  agrees 
with  the  amount  of  its  crossing-over  with  star  and  also  with  the  high 
value  (47.6)  for  squat-plexus. 

Table  130. — ^Pi,  squat    9    X  black  plexus  cf ;  B.C.,  Fi  squat    9    (-^ — ) 


hack  crossed  by  black  plexus  cf . 


Apr.  3,  1916. 

b 
Px 

b     + 
Px 

b 
Px 

b 

Px 

Total. 

No.  4044 

15  24 

3  2 

13  21 

3  1 

82 

Because  of  the  small  number  of  flies,  this  determination  is  not  very 
accurate,  but  since  the  character  is  so  poor  it  was  not  thought  best  to 
do  any  more  then,  and  the  problem  may  never  be  taken  up  again. 

A  stock  of  squat  was  made  up  and  has  since  been  running  with- 
out selection.  A  recent  (February  1918)  examination  of  the  stock 
showed  only  an  occasional  squat,  one  of  which  was  drawn  (figure  85) . 
The  original  stock  was  not  pure  and  the  present  scarcity  of  squats 
may  be  due  to  their  poor  viability  in  competition  with  the  non-squat 
sibs,  to  a  possible  lethal  nature  of  the  squat  homozygote,  and  to  some 
extent  to  "eclipse"  of  the  squat  character. 

LETHAL  Ik  SAME  AS  (/,,„). 

ORIGIN  OF  LETHAL  Ila. 

In  looking  over  the  star  black  curved  stock  (December  4,  1915)  in 
search  of  a  virgin  black  curved  female,  Bridges  noticed  that  one  of  the 
black  curved  males  had  an  eye-color  much  like  purple.  This  male  was 
out-crossed  to  a  wild  female,  and  several  pairs  of  the  wild-type  Fi 
flies  were  bred  for  the  F2  generation.  It  was  suspected  that  the  eye- 
color,  called  crimson,  was  sex-linked,  and  this  was  confirmed  by  the 
fact  that  crimson  reappeared  only  in  the  F2  males,  where  it  constituted 
about  half  the  flies.  As  soon  as  the  sex-linkage  of  crimson  was  estab- 
lished the  counts  on  the  F2  cultures  were  stopped  and  the  cultures  were 
thrown  away  in  favor  of  a  back-cross  culture,  which  had  been  made 
by  mating  the  original  crimson  male  to  one  of  his  wild-type  daughters. 
This  back-cross  culture  was  continued,  since  it  gave  crimson  females  as 
well  as  crimson  males  and  a  stock  was  directly  obtainable.  As  a  side 
issue  it  was  decided  to  make  counts  on  this  back-cross  culture  to  illus- 
trate the  independence  of  the  new  mutant  crimson  and  the  second- 
chromosome  characters.     In  making  the  counts  only  crimson  and 


OF   MUTANT    CHARACTERS. 


287 


curved  were  classified  and  no  attention  was  paid  to  black.  The  result 
was  rather  unexpected,  for  while  crimson  and  curved  jiroved  to  l^e 
independent  (56  per  cent  recombinations),  the  curved  flies  constituted 
only  31.4  per  cent  of  the  flies  instead  of  50.0  per  cent  (table  131).  Thb^ 
difference  was  not  clearly  recognized  until  the  counts  were  totaled, 

Table  131. — Pi,  dimson  black  curved  d^  X  xvild  9 ;   B.  C,  Fi  wild- 
type  9   +  crimson  black  curved  father. 


Dec.  21.  1915. 

Wild- 
type. 

Crimson. 

Curved. 

Crimiion 
curved. 

2675 

49 

69 

27 

27 

and  there  were  then  no  more  flies  hatching.  However,  one  of  these  Fj 
cultures  was  recovered  from  the  discards  and  a  count  was  taken  of  it. 
This  count  showed  no  black  curved  flies  whatever,  and  far  too  few  blacks 
and  curved.  The  case  of  dachs-lethal  was  then  being  followed,  so  that 
a  hypothesis  was  known  that  covered  this  situation.  It  was  concluded 
that  an  autosomal  lethal  had  arisen  by  mutation  in  this  second  chro- 
mosome at  a  locus  between  black  and  curved.     No  black  curved  flies 

Table  132. — Offspring  given  by  pairs  of  wild-type  flies  from  an  Fz  (Fj)  parallel 

to  the  back-cross  of  table  131. 


Jan.  15,  191G. 

Wild- 
type. 

Black. 

Curved. 

Black 
curved. 

2840 

231 
86 

8 
2 

8 
5 

1 

2863 

Total 

2861 

2864 

Total 

2859.. 

317 

10 

13 

1 

91 
2.34 

335 

110 
70 
39 

42 

6 
5 

4 

2860 

2862 

I 

5 

appeared  in  the  F2,  because  eveiy  black  curved  zygote  (except  the 
rare  double  cross-over)  was  at  the  same  time  homozygous  for  the  lethal. 

6  l  ++\ 

a '''++ 


By  crossing-over  between  black  and  the  lethal  (  -, — ; — - — > 

few  black  flies  would  be  produced  (-—- — );  likewise  the  few  curved 

\o  I  c  / 


flies  corresponded  to  crossing-over  between  the  lethal  and  curved. 
If  this  were  the  explanation,  then  most  of  the  wild-tyi)e  fli(>s  should 

be  of  the  same  constitution  as  the  Fi  flies  ( ^  j  and  wIkmi  mated 

together  should  repeat  the  F2  result.  \+  +  -|- 


288  THE    SECOND-CHROMOSOME    GROUP 

Seven  pairs  of  F2  (or  more  likely  F3)  wild-type  flies  gave  offspring 
(table  132).     Of  these  pairs,  two  (2840,  2863)  proved  to  have  both 

parents  of  the  original  constitution  f j.     Tw^o  others  (2861,  2864) 

produced  only  small  wild-type  offspring,  from  which  it  was  evident 
that  at  least  one  parent  of  each  had  carried  neither  black  nor  curved, 
and  had  come  from  the  non-crossover  chromosome  which  was  alter- 
native to  the  b  1  c  chromosome.  The  remaining  three  pairs  contained 
various  cross-over  chromosomes.     Thus,  2859  came  from 

b  -h  +  b  I  c 

r,o/>n  r  +  I   c  b  I   c  ^  b  +  c  b  I   c 

2860from  ^^-j-    j^+  -p-p-  9  ,  2862  from    ^ppq:  9  +  ipnp  d^. 


The  mother  of  2859  contained  two  cross-over  chromosomes 


\+  I  cJ 


and  must  therefore  have  been  an  F3  individual,  as  more  were  expected 

to  be. 

LOCUS  OF  LETHAL  Ila. 

The  composition  of  these  flies  is  important,  since  from  their  off- 
spring calculations  of  the  amounts  of  crossing-over  between  the  lethal 
and  both  black  and  curved  were  made.  The  first  culture  in  which  the 
lethal  appeared  (2675,  table  131)  was  of  the  type  most  advantageous 
for  the  study  of  the  crossing-over  relations  because  of  being  in  the  form 
of  a  back-cross  for  black  and  curved.  Unfortunately,  no  counts  had 
been  taken  on  black,  so  that  only  the  lethal  curved  value  could  be 
calculated.  Both  the  curved  and  the  not-curved  classes  produced  by 
this  cross  are  composite,  the  curved  class  being  composed  of  two  cross- 
overs and  a  non-crossover  class  {2x+n),  while  conversely  the  not- 
curved  class  is  2n-\-x.     The  solution  of  the  equations 

2x+n  =  54  x+2n  =  nS 

gives  x=— 3.4  and  n  =  60.7.  The  fact  that  x  has  a  minus  sign  is 
easily  accounted  for  by  probable  error,  and  only  means  that  the  loci 
of  the  lethal  and  curved  are  close  enough  together  so  that  a  small 
deviation  of  the  classes  gives  an  apparently  impossible  cross-over  value. 

In  cultures  2840  (and  2863)  the  composition  of  the  not-curved  class 
is  3n+2x  and  of  the  curved  class  simply  x.  The  not-curved  flies 
totaled  327  and  the  curved  14,  from  which  a;  =  14  and  n  =  99.7.  The 
lethal  curved  cross-over  value  is  thus  12.3.  Likewise  the  black  lethal 
cross-over  value  is  9.8.  Culture  2859  furnishes  data  on  the  lethal 
curved  value  according  to  the  equations 

3n+2a:  =  152  x  =  Q 

from  which  the  cross-over  value  is  11.4,  comparable  with  the  12.3  just 
found  from  2840H-2863.     The  condition  in  2859  with  respect  to  black 


OF    MUTANT    CHARACTERS.  2S9 

and  lethal  is  the  reverse  of  that  from  lethal  and  cun-ed,  since  black  and 
the  lethal  are  in  different  honiolojmes.     The  ecjuations  in  this  cixae  are 

2n+3xXllG  n  =  42 

from  which  the  black  lethal  value  is  20.3. 

Culture  2860  gave  a:  =  5,  n  =  20  and  a  lethal  curved  cn)s.s-ovrr  value 
of  20. 

The  foregoing  cultures  have  given  in  the  case  of  black  and  lethal  a 
total  value  of  n  of  144.7  and  of  x  of  21.7,  so  that  the  cross-over  value 
is  13.0.  Likewise  for  lethal-curved,  n  =  227.1,  x  =  2\A),  and  the  cross- 
over value  is  8.7. 

STOCK  OF  LETHAL  II  a. 

It  was  foreseen  that  stock  of  this  lethal,  which  was  called  Ictlial 
Ila  (the  "11"  designating  the  chromosome,  and  the  "a"  denoting  the 
first  of  this  series),  could  not  be  run  advantageously  by  means  of  cul- 
tures such  as  were  made  from  the  wild-type  flies  of  the  original  F,. 

A  stock  could  be  maintained  by  taking  advantage  of  the  fact  of  no 
crossing-over  in  the  male,  if  males  carrying  the  lethal  in  one  second 
chromosome  and  some  recessive  in  the  other  were  back-crossed  in  ciich 
generation  to  females  homozygous  for  this  same  recessive.  .\n  effi- 
cient scheme  for  obtaining  such  a  stock  was  devised  as  follows:  The 
original  F2  flies  appeared  only  in  the  three  classes:  wild-type,  black, 
and  curved.  The  constitution  of  any  given  wild-type  fly  could  not 
be  told  by  inspection,  but  the  case  was  different  with  the  blacks  and 
curveds.  Their  father  had  carried  black,  lethal,  and  curved  all  in  the 
same  second  chromosome,  and  since  there  is  no  crossing-over  in  a  male, 
every  sperm  which  carried  one  of  these  genes  carried  all.  Therefore 
every  black  fly  in  the  F2  should  have  the  black  lethal  curved  second 
chromosome  of  the  father. 

The  maternal  second  chromosome  is  in  this  case  a  cross-over  chromo- 
some,  carrying  black   not-lethal,  and  not-curved.     If  such   a  male 

( — ^^^  ),  were  crossed  to  a  curved  female,  the  offspring  should  be  of 
\h  I   c  / 

two  kinds — wild-type  (  — ^^^  )  and  curved  (  — —  ),  ami  every  one  of 

\H-+  c  /  \++c/ 

these  curved  flies  should  carry  the  lethal  in  the  manner  recjuired.  In- 
stead of  simple  curved,  a  black  purple  curved  plexus  speck  (tt-) 
female  was  used  in  this  out-cross— the  object  being  to  combine  the  tt  — 
stock  with  the  lua  stock  so  that  no  separate  tt-  or  l,,a  stocks  neeil  l)o 
maintained.  Three  such  out-crosses  of  Fo  black  males  to  tt-  fenuiles 
were  made.  Tvvo  of  these  gave  only  black  offsjiring  (culture  2X0'),  155 
blacks;  culture  2866,  182  blacks),  and  no  black  curved,  which  showed 
that  the  males  had  been  cross-overs  belonging  to  the  F3  generation.  To 
check  up  this  analysis,  five  Fo  cultures  were  raised  from  one  of  them 


290 


THE    SECOND-CHROMOSOME    GROUP 


(2866),  and,  as  expected,  gave  no  lethal  result  (table  133,  not  separated 
for  plexus). 

The  third  culture,  2867,  gave  40  black  curved  and  41  black  flies  and 
seemed  to  be  the  type  to  be  used.     Accordingly  several  of  the  black 


curved  males,  supposed  to  be  of  the  constitution  were  out-crossed 

0  I  c 

to  TT—  females  to  give  the  required  stable  stock.     It  was  well  that 

three  Fo  cultures  were  raised  at  the  same  time,  for  these  test  cultures 

Table  133. — Pi,  black   cf    X   black  purple  curved  plexus  speck    9 ;  Fi  black 

9  +  Fi  black  &. 


Feb.  8.  1916. 

Black 
purple 
curved 
speck. 

Black. 

Black 
purple. 

Black 
curved 
speck. 

Black 
purple 
curved. 

Black 
speck. 

Black 
purple 
speck. 

Black 
curved. 

3203 

24 
23 

27 
28 
38 

109 
214 
167 
171 
181 

4 

4 

9 

10 

21 

13 
8 
11 
15 
16 

11 
22 
21 
15 
23 

20 
16 
23 
15 

28 

2 

5 

3204  

3206 

3207 

1 

5 
3 

3208 

Total 

140 

842 

48 

63 

98 

98 

3 

13 

(table  134)  proved  that  the  male  was  not  carrying  lethal  and  had  in 

6  4-  c 
fact  been  an  F2  double  cross-over  of  the  constitution . 

+  +  t. 
After  this  failure  to  secure  stock  from  flies  of  the  original  F2,  the 

attempt  was  repeated  successfully  with  black  flies  of  the  derived 

culture  (F2)  which  had  the  same  constitution  as  the  original  F2,  but 

in  which  flies  of  the  succeeding  overlapping  generations  were  known  not 

Table  134. — Pi,  black  cf^    X  black  purple  curved  plexus  speck    9 ;  Pi  black 

curved  9  -f-  Pi  black  curved  cf. 


Feb.  7,  1916. 

Black 
purple 
curved 
speck. 

Black 
curved. 

Black 
purple 
curved. 

Black 
curved 
speck. 

3168 

3169 

34 
33 
15 

124 

123 

73 

18 

21 

9 

14 
23 

8 

3201 

Total 

82 

320 

48 

45 

to  be  present.  Two  such  black  males  by  tt  —  females  gave  as  expected 
black  and  black  curved  offspring  (3112:  6  =  81,5  c  =67;  3197:  5  =  67, 
5  c  =  53).  A  stock  from  this  source  was  turned  into  the  stock-room 
after  tests  had  shown  that  it  was  carrying  the  lethal.  The  tests  (table 
135)  consisted  of  inbreeding  some  of  the  black  curved  males  and  females, 

which  proved  to  have  the  required  constitution  {     ^^       ^"^   ^  1 . 

\h-\-lnC++/ 


OF   MUTANT   CHARACTERS. 


201 


These  tests  brought  out  the  mteresting  point  that  in  cross^'.s  in 
which  a  recessive  and  a  lethal  are  in  opposite  chromosomes  (*'       ), 

the  percentage  of  the  recessives  in  F^  is  a  constant  vahie  3:i.3, 
irrespective  of  how  much  or  how  Httle  crossing-over  there  is  between 
the  two  loci.  Thus,  the  recessives  ])urple,  plexus,  antl  si)e('k  are  at  very 
different  distances  from  the  locus  of  the  lethal,  yet  the  percentages  of 
appearance  of  all  these  is  practically  the  same  (p,  =  37.0,  p,  =  34.0, 
Sp  =  35.3,  though  sHghtly  higher  than  the  expected  value  of  33.3. 

Table  135. — The    offspring  from  pairs  of  black  curved  flies  from  lua  stock 

\b+lna-\-+)- 
[All  flies  were  black  curved  and  showed  also  the  sul)division.s  in  the  tahle.I 


Feb.  29,  1916. 

Purple 
plexus 
speck. 

"Wild- 
type." 

Purple. 

Plexus 
speck. 

Purple 
plexus. 

Speck. 

Purple 
Hpeck. 

PicXUB. 

3535 

21 
17 
24 
20 

53 
54 
65 
46 

18 
15 
22 
21 

18 
15 
18 
19 

3 

1 
1 
3 

3 

1 
3 
2 

'"4" 

2 
2 

2 

1 

3551 

3552 

3553 

Total 

82 

218 

76 

67 

8 

9 

8 

3 

TELESCOPE  (0. 

(Plate  7,  figure  6.) 

ORIGIN  OF  TELESCOPE. 

In  determining  the  locus  of  the  sex-linked  mutant  "crooked  bristles" 
(locus  38.0,  allelomorph  of  furrowed)  several  back-cross  tests  were 
made  of  females  carrying  vermilion,  crooked,  sable,  and  garnet  in  one 
X,  and  only  wild-type  genes  in  the  other.  One  of  these  tests  gave 
slightly  less  than  a  quarter  of  the  flies  with  "telescope"  abdomens 
(2735,  December  27,  1915). 

DESCRIPTION  OF  TELESCOPE. 
The  abdomens  of  the  "telescope"  flies  tend  to  retain  the  drawn-out 
appearance  that  freshly  hatched  flies  have.  The  segments  are  slightly 
separated  from  one  another  instead  of  overlapping.  The  jiigmenta- 
tion  and  chitinization  of  the  abdomen  remain  weak  and  there  is  a  wet 
(glazed)  appearance  to  the  entire  surface  of  the  body.  The  wings  droop 
at  the  sides  and  diverge,  this  character  being  very  useful  for  identifi- 
cation.    Each  band  is  sunken  at  the  middle,  with  slightly  raised  edges. 

INHERITANCE  OF  TELESCOPE. 
That  this  character  was  not  sex-linked  was  seen  at  once,  since  in 
the  culture  in  which  it  was  first  found  it  appeared  in  females  as  well 
as  males  and  showed  no  linkage  to  any  of  the  four  sex-linked  characters 


292 


THE    SECOND-CHROMOSOME    GROUP 


present.  A  mass-culture  of  the  telescope  females  and  telescope  males 
which  showed  none  of  the  sex-Unked  character  was  made  (2867). 
This  culture  failed,  probably  because  of  sterility  rather  than  from  cul- 
tural conditions,  since  some  of  these  same  flies  remated  to  purple,  in  or- 
der to  start  a  second-chromosome  linkage  test  with  telescope  failed  to 
produce  offspring  (3120,  3121,  3122).  A  second  mass-culture  of 
telescope  (2906)  produced  a  very  few  flies,  from  which  a  successful  out- 
cross  of  a  telescope  female  to  a  male  from  the  pink  spineless  stock 
(third-chromosome  recessive)  was  made  (3213;  3214  sterile).  Several 
Fi  pairs  were  started,  of  which  one  (3503)  produced  offspring.  These 
offspring  represented  a  9  : 3  : 3  : 1  ratio  of  telescope  and  pink  (+  188, 
ts  61,  p  44,  tsP  12;  disregarding  spineless),  which  proved  that  telescope 
was  not  in  the  third  chromosome. 

This  culture  furnished  (March  4,  1916)  one  of  the  most  valuable 
autosomal  characters,  hairless,  a  third-chromosome  dominant  which  is 
fully  viable  (though  lethal  when  homozygous),  which  is  easy  of  clas- 
sification, which  does  not  mask  any  other  third-chromosome  character, 
and  whose  locus  is  advantageous. 

After  the  discovery  that  telescope  was  not  in  the  third  chromosome 
it  was  thought  certain  that  it  was  in  the  second,  so  experiments 
were  planned  on  that  basis.  By  means  of  the  dominant  "star,"  at 
least  a  rough  approximation  of  the  locus  was  possible.  Accordingly 
several  out-crosses  to  star  were  made  en  masse  (3848,  3849,  3854), 
of  which  3854  alone  produced  offspring.  In  view  of  the  sterility  so 
far  encountered  it  was  thought  best  not  to  attempt  back-crosses,  but 
to  raise  F2  which  involves  the  mating  only  of  not-telescope  flies.  The 
first  tests  were  to  check  up  the  assumption  that  telescope  was  second- 
chromosome  by  means  of  a  male  test.     This  was  done  by  pairing  the 

Fi  star  males  ( j  and  Fi  wild-t3TDe  females  f  —  J.     The  telescope 

offspring,  then,  constitute  a  back-cross  test.  The  result  proved,  as 
expected,  that  the  telescope  is  second-chromosome,  for  none  of  the 
back-cross  telescopes  were  star  (table  136). 

Table  136. — Pi,  telescope  9  9  Xstar  cfcf;  Fi  star  d^  4-  ^i  wild-ttjpe9. 


Apr.  7,  1916. 

Star. 

Wild- 
type. 

Tele- 
scope. 

Star 
telescope. 

4098 

4099 

Total..,.  . 

167 
125 

55 
64 

29 
44 

0 
0 

292 

119 

73 

0 

At  this  time  the  mass  stocks  of  telescope  were  producing  better 
(4313,  4516,  4636),  so  some  female  back-cross  tests  were  attempted. 
Of  the  first  lot  one  (4400)  succeeded  fairly  well,  but  no  counts  were 


OF    MUTANT    CHARACTERS. 


293 


made.  In  the  next  generation,  however,  two  ciiltiircs  prcxluood  abun- 
dant offspring  (table  137).  Crossing-over  between  star  and  telcHcope 
was  very  free,  there  being  44.4  per  cent  observed  crossing-over  in 
a  total  of  531  flies.  By  comparison  of  this  value  with  the  other  star 
cross-over  values  it  seems  likely  that  telescoiw  is  to  the  right  of  })Inck, 
probably  to  the  right  of  purple,  and  most  probably  in  the  neighborly kkI 
of  vestigial.  A  position  at  66.5  units  to  the  right  of  star  is  given  by  a 
correction  of  the  cross-over  value,  according  to  the  i)robable  coinci- 
dence of  100. 

Table  137.— Pi,  telescope  9  9   X  star  cTcT;  B.  C,  Fy,  star  9  X  telei<cop€  cf  cf . 


May  21,  1916. 

Star. 

Tele- 
scope. 

Star 
telescai)e. 

Wild- 
type. 

4632 

4 

76 

5« 

6 

86 
65 

8 
45 
54 

3 
60 
60 

4634 

4635 

Total 

13S 

157 

107 

129 

ild- 


Time  was  men  lacking  for  testing  this  location  further.  If  the  locus 
should  be  found  to  be  to  the  right  of  curved  the  mutant  would  be 
valuable  for  some  purposes,  since  the  character  is  fairly  ea.'^y  of  cla.ssi- 
fication  and  the  sterility  seems  less  pronounced.  Pending  further 
tests,  the  stock  was  rearranged  so  that  the  dxmger  of  loss  through 
steriUty  was  eliminated  and  also  the  simple  stocks  of  purple  ami  tele- 
scope were  replaced  by  a  single  stock.  Telescope  males  (from  4634) 
were  out-crossed  to  purple  females  of  pure  stock,  and  the  Fi  wild-type 
males  were  again  out-crossed  to  purple  females.  In  the  following 
generation,  because  of  no  crossing-over  in  the  male,  only  two  chusses 

were  produced,  purple  and  wild-tvpe  (  — ,  ?^—  ).     By  mating  the  nv 

type  males  to  the  purple  females,  which  do  not  need  tfi  bo  virgin,  the 
stock  is  renewed  each  generation. 

SECOND-CHROMOSOME  "MODIFIERS"  FOR  DICH/ETE 

BRISTLE-NUMBER. 

Families  of  dichsetes  that  differ  in  mean  bristle-number  Imve  l)een 
established  by  Sturtevant  through  selection  (August  3,  1016).  That 
these  differences  are  in  part  due  to  one  or  more  secontl-chromosome 
modifying  genes  has  been  shown  by  the  following  method: 

A  dichajte  of  a  selected  line  was  crossed  to  speck  of  a  stock  tliiit  had 
been  long  and  closely  inbred  in  order  that  it  might  become  homozygous. 
Dichsete  being  dominant,  half  of  the  offspring  were  diclnete,  and  all  of 
them  were  heterozj^gous  for  speck.  The  Fi  dichiete  males  were  then 
back-crossed  to  speck  females.  They  producetl  diciuete  offsjiring  t  hat 
were  not-speck  and  as  many  others  that  were  speck:  from  their  fatlier 


294 


THE    SECOND-CHROMOSOME    GROUP 


these  two  classes  of  offspring  received  second  chromosomes  that  came 
from  the  two  original  stocks.  If  those  original  stocks  differed  in 
second-chromosome  modifiers  the  two  classes  should  differ  in  mean 
bristle-number.  This  has,  in  fact,  been  found  to  be  the  case  (see  below) . 
But  if  an  Fi  female  is  used,  these  differences  should  be  less  than  in  the 
above  case,  provided  the  modifier,  or  modifiers,  crossed  over  from 
speck.  This  result  has  also  been  obtained,  as  will  appear  from  table 
138,  which  shows  the  excess  in  mean  bristle-number  of  the  not-specks 
over  the  specks  among  the  dichsete  offspring  from  back-crosses  of  the 
type  described  above.  The  two  values  in  any  one  line  are  from  the 
same  combination  of  stocks,  and  are  therefore  available  for  comparison 
of  male  tests  with  female  tests. 


Table  138. 

Test  of  Fi(f . 

Test  of  Fi  9  . 

+  .852=fc.067 
+  .192±.040 
+  .439±.132 
+  .545±.091 
+  .345±.113 
+  .542±.133 
+  .202=fc.081 

+  .150±.128 
+  .088±.093 
+  .367=fc.073 
-.054±.055 
-.259  ±.125 
-.532±.180 

These  data  demonstrate  the  existence  of  one  or  more  second-chromo- 
some modifiers  for  dichsete  bristle-number,  and  show  that  at  least  one 
such  modifier  crosses  over  from  speck. 

Further  details  and  conclusions  of  this  selection  experiment  and  a 
general  discussion  of  the  subject  are  given  by  Sturtevant  in  Carnegie 
Institution  of  Washington  Publication  No.  264. 


DACHSOID. 

(Text-figure  86.) 

ORIGIN  OF  DACHSOID. 

In  testing  for  the  presence  of  a  third-chromosome  cross-over  variation 
reported  to  be  present  in  the  eosin  stock,  Sturtevant  out-crossed  two 
eosin  males  separately  to  females  from  the  stock  containing  the  third- 
chromosome  recessives  sepia,  spineless,  kidney,  sooty,  and  rough. 
Several  of  the  daughters  from  each  of  these  matings  were  back-crossed 
to  males  from  the  multiple  recessive  stock.  This  experiment  is  dis- 
cussed by  Sturtevant  in  the  paper  appearing  herewith  (Part  III) .  From 
both  series  brother-sister  pairings  of  the  back-cross  type  were  continued 
through  several  generations.  "Dachsoid,"  a  new  mutant  wing-type, 
appeared  in  four  out  of  seven  of  the  inbred  cultures  of  F2  in  one  strain 
(from  2568a).     The  first  of  these  was  observed,  February  9,  1917,  in 


OF    MUTANT    CHARACTERS. 


295 


culture  2671  (A.  H.  S.).     The  rolationshij)  between  the  first  cultures 
in  which  the  character  was  observed  is  shown  in  the  foUowiuK  ix'digree: 


2568a   (8,8gke»roXw«) 


1 — 
2608 


2610 


2613 


2614 


2671*     2686*      2713*       2667      2694*      2700 


2615  2617       ::S6«aX 

(Waa-typc  » 
2672  ♦."*, Sjkc'ro 

bl  i.tlK-r  P 


The  four  cultures  starred  in  the  above  diagram  gave  the  following 
numbers  of  offspring: 

Table  139. 


Culture. 

Not- 
dachsoid. 

Dachsoid. 

Total. 

2671 

2686 

2694 

2713 

Total .  . 

52 
110 
184 
146 

7 

7 

10 

17 

59 
117 
203 
103 

492 

50 

542 

The  viability  of  the  dachsoid  flies  was  evidently  very  poor;  and  the 
adults  were  so  weak  that  all  attempts  to  breed  from  thoin  failed.  For 
this  reason  the  character  was  discarded  after  very  little  had  l)oon  done 
with  it. 

Since  three  daughters  of  the  original  pair  produced  dachsoid  descend- 
ants w^hen  mated  to  different  stock  males,  it  is  practically  certain  that 
one  of  the  parents  of  2568a  (A.  H.  S.)  was  heterozygous  for  the  dach- 
soid gene.  It  is  not  possible  to  determine  which  parent,  or  how  long 
the  character  had  been  in  the  stock.  No  other  experiments  involving 
these  (or  any  other)  stocks  have  produced  dachsoid  flies. 

DESCRIPTION  OF  DACHSOID. 

As  show^n  in  figure  86,  the  dachsoid  flies  are  small  and  all  parts— he^id 
thorax,  abdomen,  wings,  and  legs — are  markedly  shortened,  iis  though 
from  pressure.  The  particular  specimen  drawn  was  sepia  spineless 
kidney  sooty  rough,  as  well  as  dachsoid,  and  the  short  bristles  and 
abnormal  eyes  are  due  not  to  the  dachsoid  but  to  spineless  and  kidney 
rough.  The  wings,  besides  being  shortened,  are  actually  broader  than 
normal.  They  are  held  out  at  a  wide  angle  from  the  body  and  have 
a  tendency  to  curve.  The  posterior  cross-vein  is  almost  entirely  gone 
and  frequently  the  anterior  cross-vein  is  similarly  affected.  .V  char- 
acteristic feature  is  a  short  branch  on  the  second  longitudinal  vein 
similar  to  the  remnants  of  the  cross- veins.  The  hairs  on  the  costal 
vein  before  the  apex  of  the  first  vein  stand  out  from  the  vein  more  than 
in  wild-type  flies. 


296 


THE    SECOND-CHROMOSOME    GROUP 


CHROMOSOME  CARRYING  DACHSOID. 

The  four  cultures  above  noted  (table  139)  all  gave  both  male  and 
female  dachsoids,  thus  showing  at  once  that  the  gene  is  not  in  the  X 
chromosome.  The  mothers  of  all  four  were  heterozygous  for  sepia, 
spineless,  kidney,  sooty,  and  rough — characters  that  cover  practically 
the  whole  length  of  the  third  chromosome,  and  the  same  was  true  of 
several  later  cultures  that  also  gave  dachsoid.  The  dachsbid  char- 
acter was  distributed  quite  at  random  with  respect  to  these  third- 
chromosome  characters,  showing  that  the  gene  is  not  in  the  third 
chromosome. 


Text-figure  86. — Dachsoid  venation.     860  shows  the  small  size  of  the  flj',  with  the  wing  pos- 
ture; 866  shows  a  typical  wing. 

An  F3  from  a  cross  between  speck  and  a  fly  that  proved  to  be  heter- 
ozygous for  dachsoid  produced  15  dachsoid,  but  unfortunately  the 
speck  character  was  not  examined  (2859,  A.  H.  S.). 

An  F3  pair  (2926)  gave  a  total  of  40  flies,  of  which  4  were  dachsoid, 
26  speck,  10  wild-type,  and  none  dachsoid  speck.  The  count  was 
aberrant  in  that  there  were  far  too  few  wild-type  offspring;  but  the 


OF    MUTANT    CHARACTERS.  207 

probability  is  that  the  gene  is  in  the  second  chromosonio,  especially  in 
view  of  the  evidence  that  it  is  not  in  the  X  or  third  chromosome. 

As  is  suggested  in  its  name,  dachsoid  has  certain  points  of  resem- 
blance to  the  second-chromosome  character  dachs.  It  was  therefore 
surmised  that  the  gene  might  be  allelomorphic  to  the  dachs  gene,  and 
the  following  tests  were  made: 

Six  offspring  of  the  four  pairs  in  which  dachsoid  first  apj^eared 
were  selected  at  random.  Two-thirds  of  these  would  be  expect^'d  to 
be  heterozygous  for  dachsoid;  and  the  chance  that  none  was  hetero- 
zygous is  only  l-j   =^-     These  6  individuals  were  then  mated, 

some  to  homozygous  dachs,  some  to  flies  heterozygous  for  dachs.  All 
produced  a  considerable  number  of  offspring  (105  to  199  per  pair)  and 
another  similar  mating  (to  homozygous  dachs)  produced  9  ofTsjiring. 
None  of  the  Fi  flies  showed  any  trace  of  the  characteristics  of  dachs  or 
dachsoid,  or  any  other  unusual  characters.  It  therefore  follows  that 
the  flies  heterozygous  both  for  dachs  and  for  dachsoid  are  normal  in 
appearance.  In  all  probability,  therefore,  the  genes  of  the  two  char- 
acters are  not  allelomorphic. 

THE  CONSTRUCTION  OF  THE  MAP  OF  THE  SECOND 

CHROMOSOME. 

The  map  given  on  page  127  is  constructed  on  the  basis  of  the  total 
data  available  on  each  cross-over  value.  The  first  step  taken  was  to 
collect  and  summarize  this  data  in  the  form  in  which  it  appears  in 
table  140. 

In  constructing  the  map  of  the  second  chromosome  on  the  basis  of 
all  the  available  data,  the  procedure  was  roughly  as  follows:  The 
first  locus  to  be  considered  was  that  of  black,  since  the  "second"  chro- 
mosome had  originally  been  defined  quite  arbitrarily  as  that  chromo- 
some which  carries  the  gene  for  black  and  siich  other  genes  as  may  be 
found  to  be  linked  to  black,  while  correspondingly  the  third  chromasome 
was  that  chromosome  which  carries  the  gene  for  pink  and  such  other 
genes  as  may  be  found  to  be  linked  to  pink.     Furthermore,   it  so 
happened  that  of  the  early  rnutations  which  were  stably  mapi>od 
(black,   purple,    vestigial,   and   curved)    black   was   the   one   located 
farthest  to  the  left,  and  was  therefore  chosen  as  the  zero-jioint  of  this 
early  map.     Even  after  black  had  been  displaced  from  the  i)osition 
at  zero,  it  still  remained  the  base  of  reference  of  the  entire  second 
chromosome,  in  relation  to  which  all  other  loci  are  mapi>ed,  either 
directly,  in  the  case  of  those  close  by,  or  indirectly,  through  refer- 
ence to  intermediate  bases  in  the  case  of  those  farther  away.     Bhick 
was  therefore  accepted  as  the  constructional  zero-point  of  the  maji, 
and  all  other  loci  were  to  be  mapped  as  lying  to  the  right  or  to  the  left 
of  black  by  a  specific  number  of  units.     The  loci  to  the  right,  or  in  a 


298 


THE    SECOND-CHROMOSOME    GROUP 


plus  direction  from  black,  were  those  lying  on  the  same  side  of  black 
as  does  curved,  which  was  the  first  locus  to  be  included  with  black  in 
the  second  chromosome.  Likewise  the  loci  "to  the  left,"  or  in  a 
minus  direction,  were  those  lying  on  the  opposite  side  of  black  from 
curved. 

However,  curved  is  too  remote  from  black  to  be  accurately  located 
by  direct  reference  to  black.     Accordingly,  the  position  of  these  inter- 

Table  140. — Summary  of  available  data  on  crossing-over  in  the  second 

chromosome. 


Loci. 


Star  streak 

Star  cream  b 

Star  truncate. ... 

Star  black 

Star  apterous 

Star  purple 

Star  vestigial 

Star  curved 

Star  trefoil 

Star  telescope . .  .  . 

Star  plexus 

Star  fringed 

Star  pinkish 

Star  speck 

Streak  dachs 

Streak  black 

Streak  purple 

Streak  vestigial. . . 
Streak  curved . . .  . 
Streak  blistered. . . 

Streak  speck 

Streak  balloon . . . . 
Streak  morula . . . . 

Dachs  black 

Dachs  purple 

Dachs  vestigial . . . 
Dachs  curved.  .  .  . 

Dachs  speck 

Dachs  balloon . . . . 

Sfjuat  black 

Squat  plexus 


Total. 


16, 

8, 

19, 

1, 


2, 
2, 


6, 
1, 
5, 


396 
389 

549 
507 
169 
155 
450 
870 
154 
531 
352 
496 
175 
135 
858 
462 
665 
462 
269 
11 
462 
462 
876 
725 
489 
354 
462 
462 
462 
82 
82 


Cross- 
overs. 


63 

86 

149 

6,250 

83 

3,561 

195 

9,123 

65 

236 

632 

274 

74 

3,448 

109 

120 

883 

164 

923 

5 

242 

242 

405 

1,196 

293 

1,585 

145 

231 

231 

9 

39 


Per 
cent. 


15.9 
22.1 
27.1 
37.9 
49.0 
43.7 
43.3 
45.9 
42.2 
44.4 
46.7 
55.2 
42.3 
48.3 
12.7 
26.0 
33.1 
35.5 
40.7 
45.0 
52.3 
52.3 
46.3 
17.8 
19.7 
29.6 
31.4 
50.0 
50.0 
11.0 
47.6 


Loci. 


Black  jaunty. . . . 
Black  purple .... 
Black  lethal  Ila . 
Black  vestigial .  . 

Black  curved 

Black  plexus. .  .  . 
Black  fringed  .  .  . 

Black  arc 

Black  blistered. . 
Black  pinkish ... 

Black  speck 

Black  balloon ... 
Black  morula  . .  . , 
Purple  vestigial . . 

Purple  curved 

Purple  plexus. . . . 

Purple  arc , 

Purple  speck 

Purple  balloon .  .  . 
Lethal  IIo  curved 
Vestigial  curved . . 
Vestigial  speck .  . . 
Vestigial  balloon., 
Curved  speck .  .  . . 
Curved  balloon . . 

Plexus  speck 

Arc  speck 

Arc  morula 

Blistered  speck . . . 
Speck  balloon . .  .  . 


Total. 


462 

48,931 

166 

20,153 

62,679 

2,460 

496 

7,592 

224 

736 

685 

2,236 

7,549 

13,601 

51,136 

344 

2,625 

11,985 

462 

249 

1,720 

2,054 

462 

10,042 

462 

.327 

2,625 

6,794 

36 

462 


Cross- 
overs. 


Per 

cent. 


1? 

3,026 

22 

3,578 

14,237 

1,031 

211 

3,2.37 

93 

371 

326 

1,073 

3,518 

1,609 

10,205 

164 

1,066 

5,474 

218 

22 

141 

738 

178 

3,037 

150 

29 

156 

634 

3 

2 


0.2? 

6.2 
13.0 
17.8 
22.7 
41.9 


42 

42 

41 

51 

47.6 

48.1 

46.6 

11.8 

19.9 

47.7 

40.6 


45 

47 

8 

8 

35 

38.5 

30.2 

32.5 

8.9 

5.9 

7.9 

8.3 

0.4 


mediate  bases  must  first  be  mapped.  Of  these,  purple  was  the  first 
to  be  considered  as  being  the  closest  to  black,  and  also  because  its 
position  with  relation  to  black  has  been  the  subject  of  more  investi- 
gation, and  is  more  accurately  determined  than  any  other  second- 
chromosome  distance.  The  black  purple  cross-over  value  of  6.2  is 
based  on  48,931  flies,  and  since  there  is  certainly  no  double  crossing- 
over  within  this  distance,  the  value  can  be  accepted  without  correction, 
and  purple  can  be  mapped  at  a  locus  6.2  units  to  the  right  of  black. 

The  third  locus  to  be  considered  is  vestigial,  and  there  are  open  two 
sets  of  data  by  means  of  which  the  position  of  vestigial  can  be  mapped : 
(1)   the  position  of  vestigial  can  be  located  directly  by  the  purple 


OF   MUTANT    CHARACTERS.  299 

vestigial  cross-over  value  of  11.8;  that  is,  vestigial  is  11.8  unit«  to  the 
right  of  purple  or  at  18.0  to  the  right  of  l)lack.  This  location  is  hjisod 
on  a  total  of  13,601  flics  for  the  jMirpIe  vestigial  cross-over  value- 
(2)  but  there  are  available  20,153  flics  giving  a  black  vestigial  cross- 
over value  of  17.8.  This  distance  is  long  enough  so  that  donblo 
crossing-over  occurs  within  it,  and  the  cross-over  \-aliie  nuist  therefore 
be  corrected.  The  black  purple  vestigial  and  other  back-cro.ss  experi- 
ments by  which  the  amount  of  this  double  crossing-over  has  been 
measured  show  that  the  amount  of  such  double  crossing-over  is  rela- 
tively very  high,  the  probable  coincidence  being  about  00.  The  cor- 
rected value  corresponding  to  a  given  coincidence  and  an  observjHl 
cross-over  value  can  be  calculated  closely  enough  for  our  present 
purposes  by  aid  of  the  following  equation : 


2       X  o 

x^  — 


C        2C 

in  which  C  =  the  given  coincidence,  o  =  the  observed  cross-over  value, 
and  2a:  =  the  corrected  distance,  all  expressed  a«  decimal  fractions 
rather  than  as  percentages.  The  correction  corresponding  to  a 
coincidence  of  60  amounts  to  about  1.1  units  on  an  observed  value  of 
17.8,  so  that  the  locus  of  vestigial  is  18.9  units  to  the  right  of  black  on 
the  basis  of  the  black  vestigial  data.  However,  the  precision  of  the 
location  based  on  values  that  must  be  corrected  decreases  rapidly  with 
the  increase  in  the  size  and  consequent  uncertainty  of  the  correction. 
Although  the  position  of  vestigial  at  18.9  is  based  on  20,168  flies,  the 
value  of  each  fly  represented  in  the  black  vestigial  cross-over  data  is 
not  as  great  as  the  value  of  each  fly  in  the  purple  vestigial  exj)erinients, 
where  the  coincidence  is  probably  zero  and  no  correction  at  all  need 
be  made.  Roughly,  the  black  vestigial  data  should  be  weighted  about 
three-quarters  of  its  face  value  as  compared  with  the  j)urple  vestigial 
data.  By  combining  the  two  sets  of  approximately  weighted  daUi, 
the  mean  position  of  the  vestigial  locus  is  found  to  be  18.5  units  to  the 
right  of  black. 

The  position  of  curved  is  reached  by  a  combination  of  three  sets  of 
weighted  data:  The  most  direct  data,  which  needs  no  correction,  is 
that  derived  from  the  vestigial  curved  cross-over  value  of  S.2  units 
based  on  1,720  flies.  According  to  this  data,  the  position  of  curved 
is  at  18.54-8.2,  or  26.8  units  to  the  right  of  black.  The  next  most 
direct  method  of  location  is  by  reference  to  purple,  the  purple  curved 
cross-over  value  of  19.9  being  based  on  51,136  flies.  This  value  needs 
correction  according  to  the  probable  coincidence  of  70  b}'  the  addition 
of  1.5  units,  which  gives  a  locus  21.4  units  to  the  right  of  iKirj)le.  or 
27.6  units  to  the  right  of  black.  The  number  of  flies  is  to  be  r:i{od  at 
about  70  per  cent  of  its  face  value,  or  at  about  3S,S00  flies.  The  third 
method  is  by  means  of  the  black  curved  cross-over  value  of  22.7  cor- 


300  THE    SECOND-CHROMOSOME    GROUP 

reeled  to  26.2  according  to  the  probable  coincidence  of  100,  and 
weighted  at  50  per  cent  of  the  62,679  flies  (31,340) .  The  mean  position 
of  curved  is  27.0  units  to  the  right  of  black. 

The  fifth  locus  to  be  considered  is  that  of  dachs,  which  lies  to  the 
left  of  black.     The  dachs  black  data  give  a  cross-over  value  of  17.8 
corrected  to  18.5  according  to  the  probable  coincidence  of  50  and 
weighted  at  about  80  per  cent  of  the  6,725  flies  (5,380).     The  dachs 
purple  value  of  19.7  is  corrected  to  21.1,  according  to  a  probable 
coincidence  of  60  and  weighted  at  about  75  per  cent  of  the  1,489  flies 
(1,150).     The  locus  is  thus  at  6.2-21.1,  or  -14.9.     The  coincidence 
in  the  case  of  dachs  vestigial  is  known  to  be  about  85,  so  that  the  value 
of  29.6  can  be  corrected  accurately  to  34.6,  corresponding  to  a  locus  of 
— 16.1  and  weighted  at  about  30  per  cent  of  the  5,354  flies  (1,605).     The 
mean  locus  of  dachs  is  thus  17.5  units  to  the  left  of  black,  or  at  —17.5. 
With  the  mapping  of  the  positions  of  the  four  genes,  black,  purple, 
vestigial,  and  curved,  and  also  the  position  of  dachs,  which  lies  to  the 
left  of  black,  the  skeleton  of  what  may  be  called  the  central  body  of 
genes  is  completed.     The  next  step  is  to  tie  onto  this  central  group  the 
outlying  loci  at  either  end.     Of  those  to  the  left,  streak  is  the  most 
important  locus,  and  its  position  is  found  by  combining  three  sets  of 
data.     The  streak  dachs  cross-over  value  of  12.7,  based  on  858  flies, 
needs  no  correction,  since  the  probable  coincidence  is  under  10  and  the 
correction   negligible   in   amount.     The   streak  black   value   of  26.0 
should  be  corrected  to  about  28.2,  corresponding  to  a  coincidence  of 
60,  and  wdth  the  462  flies  weighted  at  65  per  cent,  i.  e,  307.     The  most 
extensive  data  is  that  on  streak  purple,  but  the  2,665  flies  should  be 
weighted  at  only  about  50  per  cent  of  their  number,  or  at  1,333.     The 
coincidence  is  probably  about  90,  so  that  the  value  of  33.1  becomes 
40.4,  corresponding  to  a  locus  of —  34.2.     The  mean  position  of  streak 
is  at  —31.1. 

The  position  of  star  is  15.9  units  to  the  left  of  streak  or  at  —47.0, 
according  to  the  star  streak  cross-over  value  of  15.9,  which  needs  no 
correction.  The  star  dachs  value  of  27.3  is  corrected  to  28.8,  according 
to  the  probable  coincidence  of  30.  The  locus  indicated  is  46.3  units 
to  the  left  of  black.  The  3,472  flies  may  be  rated  at  about  80  per  cent 
of  their  number,  or  at  2.778.  The  star  black  value  of  37.9  probably 
represents  a  total  of  46. o  per  cent  of  crossing-over,  with  a  coincidence 
of  90,  and  the  16,507  flies  may  be  rated  at  about  35  per  cent  of  the 
number,  or  at  5,775.     The  mean  position  of  star  is  thus  at  —46.5. 

The  location  of  all  the  right  end  is  dependent  on  speck,  which  is 
itself  mainly  dependent  on  curved.  The  curved  speck  value  is  30.5 
and  the  coincidence  is  known  to  be  very  low  in  this  region,  probably 
not  over  20,  so  that  the  corrected  value  is  about  31.0.  Because  of  this 
low  coincidence  a  relatively  large  weighting  can  be  assigned  (85  per 
cent  =  8,540).     The  vestigial  speck  data  furnish  2,054  flies  weighted 


OF   MUTANT    CHARACTERS.  301 

at  about  80  per  cent,  and  a  cross-over  value  of  35.9  corrected  to  37.G 
according  to  the  probable  coincidence  of  30.  The  net  coincidence  in 
the  case  of  purple  speck  is  about  50,  so  that  the  value  of  45.7  niiiy  l>e 
corrected  to  53.6,  with  a  locus  of  59.8  The  wcij^htin^  correspondirin 
to  this  distance  and  coincidence  is  about  70  jut  cent,  or  there  is  the 
equivalent  of  8,390  flies.  The  mean  position  for  the  locus  of  speck  is 
at  about  58.6  units  to  the  right  of  l)lack. 

The  establishment  of  the  foregoing  loci  complete  what  may  \>o  called 
the  *'triangulation"  for  the  map  of  the  second  chromosome.  The 
remaining  loci  are  filled  in  secondarily  with  relation  to  one  or  more  of 
these  bases,  or  in  the  case  of  a  few,  the  relation  to  still  other  loci  must 
be  considered.  Thus  the  position  of  morula  is  dejiendent  primarily 
on  the  position  of  arc,  which  must  first  be  located.  The  moan  position 
of  arc  is  found  by  means  of  the  arc  speck  value  of  5.9  based  on  2,('»'J5 
flies,  the  purple  arc  value  corrected  to  44.2  (('  =  40)  and  weighted  at 
1,838.  the  black  arc  value  corrected  to  52.1  (C  =  70)  and  weighted  at 
3,038,  to  be  51.9  units  to  the  right  of  black  or  —6.7  from  speck. 

The  position  of  morula  at  black  -f  59.8  is  based  entirely  on  the  arc 
morula  value  of  7.9  found  from  6,794  flies. 

The  remaining  loci  \vill  be  treated  very  briefly  in  the  order  of  their 
appearance. 

The  locus  of  olive  is  not  exactly  known,  nor  is  it  important.  The 
probability  is  that  it  lies  to  the  right  of  speck  and  not  more  than  a  unit 
distant,  or  at  106.1  referred  to  star. 

The  locus  of  truncate  is  best  found  from  the  star  truncate  value  of 
27.1  corrected  to  28.0  (C  =  25),  which  give  a  position  28  units  to  the 
right  of  star. 

The  locus  of  balloon  is  0.4  unit  to  the  right  of  speck  (S'  + 105.5), 
based  on  462  flies. 

The  locus  of  the  lethal  hypothecated  in  the  chromosome  homologous 
to  that  carrying  truncate  (lethal  T')  is  probably  within  15  units  of  the 
truncate  locus  as  judged  from  the  proportion  of  wild-type  and  truncate 
flies  in  the  highly  selected  stocks. 

The  locus  of  bhstered  is  approximately  2  units  to  the  left  of  si)eck 
(or  at  S'  +  103)  as  deducted  from  the  qlistered  speck  cross-over  value 
and  certain  later  indications. 

The  locus  of  jaunty  is  very  close  to  that  of  black,  probably  0.2  unit 
to  the  right  (S'-f  46.7),  on  the  basis  of  one  questionable  cross-over  in 
Muller's  progeny  tests. 

Strap,  antlered,  and  nick  are  probably  allelomorphs  of  vestigial  with 
the  same  locus  (S'  +  65.0).  If  they  are  not  allelomorphs,  then  their 
loci  are  so  close  to  that  of  vestigial  that  the  interval  is  negligible. 

The  locus  of  gap  is  suspected  of  being  in  the  neighboriiood  of  curved. 

The  locus  of  comma  is  perhaps  =<=  15  units  from  that  of  squat 
(Sq'  =  S-f  35.5),  as  judged  roughly  from  the  distribution  of  squat  and 
comma. 


w 


302  THE    SECOND-CHROMOSOME    GROUP 

The  locus  of  apterous  is  about  2  units  to  the  right  of  black,  or  at 
approximately  48.8. 

Cream  II  and  patched  were  found  to  be  linked,  but  their  positions 
with  respect  to  the  other  loci  were  not  found. 

The  position  of  trefoil  is  around  50  units  from  star. 

The  corrected  star  cream  h  value  of  22.5  gives  the  locus  of  cream  b 
directly. 

The  gene  for  pinkish  is  located  in  the  far  right  end  of  the  chromosome, 
but  the  locus  has  not  been  accurately  determined. 

The  plexus  speck  value  of  8.7  is  at  present  the  only  acceptable  infor- 
mation on  the  precise  location  of  plexus,  which  is  thus  at  a  locus  of  96.2. 

' ' ' 1 ' n-T^H 'ill' — I ' ' 1  II  '     I  jiir: 


O  ifk  in  b  b  in  i"  "~Ju'l'+    s  in    b  u'  w  n  b>i» 


MWm^-u. 


© 


'^'  K  Cd)       S^  0       (S)  W"^  c  f/-^a 


1 1  r 


na  (fp) 


crb     T'  aip^tf  tg 


Text-figure  87. — Constructional  map  of  second  chromosome,  giving  bases  of  reference  and 
indicating  various  cross- over  values  used  in  calculating  mean  position  for  each  locus. 

The  locus  of  limited  is  either  the  same  as  that  of  morula,  which  is 
possible,  or  is  slightly  to  the  right. 

The  black  fringed  value  of  42.5  is  almost  the  same  as  the  black  arc 
value  of  42.6,  so  that  we  may  place  fringed  at  98.0. 

The  locus  of  dachs-lethal  is  probably  the  same  as  that  of  dachs, 
29.0  (dachs-deficiency) ;  but  if  this  is  not  the  case,  then  the  locus  is  so 
close  to  that  of  dachs  that  the  interval  is  negligible. 

Squat  gave  11.0  per  cent  of  crossing-over  with  black  and  can  there- 
fore be  mapped  at  35.5. 

Lethal  Ila  gave  a  value  of  13.0  with  black,  and  a  value  of  8.7  with 
curved.  In  the  first  case  there  were  166  flies,  indicating  a  position  of 
59.5;  and  in  the  second  case  249  flies,  indicating  a  position  at  64.8. 
The  mean  position  is  thus  62.7. 

The  position  of  telescope  is  known  only  from  the  star  telescope 
back-cross  value  of  44.4,  which  indicates  a  locus  at  about  66.5  (C  =  100). 

The  loci  of  the  various  mutant  genes  with  respect  to  black  as  a  base 
of  reference  have  just  been  found.  In  some  regards  it  is  more  con- 
venient to  renumber  these  loci  so  that  the  left-most  (star)  is  taken  as 


OF   MUTANT    CHARACTERS. 


303 


^£> 


O  0 


Mz- 


®a 


^3. 


-<DflY 


z^ 


tz  % 


IB  O 
£9  O 


3Sft 


■MS 

■MS 

soot 


M 


the  zero-point  and  the  others  have  consecutive  numbers  in  a  sinj^le 
series.     The  map  made  in  this  waj'  has  already  been  given  on  page  127. 

In  using  such  a  map  one  should  keep  in  mind  botli  the  locus  iiK  given 
and  the  manner  in  which  that  locus 
has  been  established,  since  this  largely 
determines  not  only  the  accuracy  but 
also  the  significance  of  any  particular 
location. 

A  type  of  diagram  which  is  capable 
of  representing  fully  the  relationship 
of  each  locus  to  the  other  loci  is  given 
in  text-figure  87. 

This  diagram  could  be  further  elab- 
orated by  making  the  heaviness  of  line 
correspond  to  the  accuracy  of  data, 
and  by  giving,  besides  the  final,  the 
reference-base  positions.  Thus  pr  vg 
gives  a  locus  of  vestigial  at  6-^18.0, 
while  the  corrected  black  vestigial  data 
indicate  a  locus  of  vestigial  at  64-18.9, 
while  the  locus  actually  given  in  the 
diagram  is  the  mean  position  for  ves- 
tigial at  18.5 

The  type  of  map  which  is  in  daily  use 
in  our  laboratory  is  that  given  in  text- 
figure  88,  in  which  the  loci  are  further 
classified  according  to  the  value  of  the 
character,  etc.  Thus,  the  mutants  of 
first  rank  in  value  are  made  conspic- 
uous and  insured  first  consideration  by 
being  lined  up  at  the  extreme  left  edge 
of  the  space.  The  mutants  nearly  as 
good,  but  whose  usefulness  is  restricted 
in  one  or  another  respect,  are  spaced 
next  in  order.  Still  further  to  the  right 
are  those  whose  loci  are  not  well  estab- 
lished or  whose  characteristics  are  such 
that  they  are  useful  only  in  experiments 
of  a  very  special  nature.  At  the  ex- 
treme right  are  the  mutants  no  longer 
available,  because  the  stocks  have  been 
lost  or  discarded.  This  type  of  map  can 
be  kept  subject  to  continuous  changes 
in  the  valuations  or  the  locations  of  the 
different  mutants  by  drawing  the  map-scale  on  a  soft  board  and 
mounting  the  symbols  for  each  mutant  on  the  head  of  a  thumb-tack. 


10 


20 


30 


40 


50 


60 


70 


80 


90 


100 


no 


=t> 


6&.0 
6«S 


::-  73  i 


Text-fiqure  88. — Workinn  and  valua- 
tion map  of  the  .soroiul  rhroniowmio. 
The  loci  niappod  at  tho  left  margin  n't>- 
resont  tho  niont  valuable  ni«taMf."«. 
tho!<o  farther  to  tho  ri^ht  pri>KroH!»ivrly 
Icsa  u»oful.  Thoso  next  tho  riuht 
niarKin  are  niutant.s  no  longer  ext&iit. 


BIBLIOGRAPHY. 

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,  Jan. -Mar.,  1916.     Non-disjunction  as  proof  of  the  chromosome  theory  of    eredity" 

Genetics,  1 :  1-52,  107-163. 

,  Sept.,  1917.     Deficiency.     Genetics,  2:  445-465. 

,  and  A.  H.  vSturtevant,  Apr.,  1914.  A  new  gene  in  the  second  chromosome  of  Dro- 
sophila, and  some  considerations  on  differential  viability.     Biol.  Bull.,  26:  205-213i 
Hyde,R.R.    Dec,  1913.    Inhcritanceof  the  length  of  life  in  Drosop/iiJaampeiopMo.    Report, 
Indiana  Acad,  of  Sci.,  113-123. 

,  July,  Aug.,  Oct.,  1914.     Fertility  and  sterility  in  Drosophila  ampelophila.     J.  E. 

Z.,  17:  141-171,  173-212,  343-372. 
Jennings,  H.  S.     May,  1917.     Modifying  factors  and  multiple  allelomorphs  in  relation  to 

the  results  of  selection.     Am.  Nat.,  51:  301-306. 
LiFF,  Joseph.     Feb.,  1915.     Data  on  a  pecuhar  MendeUan  ratio  in  Drosophila  ampelophila. 

Am.  Nat.,  49:97-120. 
LuTZ,  F.  D.     Feb.,  1913.     Experiments  concerning  the  sexual  differences  in  the  wing-length 

of  Drosophila  ampelophila.     J.  E.  Z.,  14:  267-273. 
MacDowell,  E.  C.     July,  1915.     Bristle  inheritance  in  Drosophila.     J.  E.  Z.,  19:61-98. 
Marshall,  Walter  W.,  and  H.  J.  Muller.     Feb.,  1917.     The  effect  of  long-continued 

heterozygosis  on  a  variable  character  in  Drosophila.     J.  E.  Z.,  22:457-470. 
Metz,  Chas.  W.     Nov.,  1914.     An  apterous  Drosophila  and  its  genetic  behavior.     Am. 
Nat.,  48:  675-692. 

,  and  B.  S.  Metz.     Mar.,  1915.     Mutations  in  two  species  of  Drosophila.     Am.  Nat., 

49: 178-189. 
Morgan,  T.  H.     May,  1910.     Hybridization  in  a  mutating  period  in  Drosophila.     Proc. 
Soc.  Exp.  Biol,  and  Med.,  7:  160-162. 

,  Mar.,  1911.  The  origin  of  nine  wing  mutations  in  Drosophila.   Science,  33:  496-499. 

,  July,  1912.     Heredity  of  body-color  in  Drosophila.     J.  E.  Z.,  13:  27-45. 

,  Nov.,  1912.     Further  experiments  with  mutations  in  eye-color    of    Drosophila. 

Jour.  Acad.  Nat.  Sci.,  Phila.,  321-350. 
,  Nov.  22,  1912.     Complete  linkage  in  the  second  chromosome  of  the  male  of  Dro- 
sophila.    Science,  36:  4-6. 

,  Apr.,  1914.     No  crossing-over  in  the  male  of  Drosophila  of  genes  in  the  second  and 

third  pairs  of  chromosomes.     Biol.  Bull.,  26:  195-204. 

,  July,  1914.     Two  sex-linked  lethal  factors  in  Drosophila  and  their  influence  on  the 

sex-ratio.     J.  E.  Z.,  17:  81-122. 

,  July,  1915.     The  role  of  the  environment  in  the  realization  of  a  sex-linked  Men- 

dehan  character  in  Drosophila.     Am.  Nat.,  49:  345-429. 

,  Oct.,  1916.     A  critique  of  the  theory  of  evolution.     Princeton  Univ.  Press,  195  pp. 

,  and  C.  B.  Bridges.     May,  1916.     Sex-linked  inheritance  in  Drosophila.     Carnegie 

Inst.  Wash.  Pub.  No.  237,  1-87. 

,  and  Clara  J.  Lynch.     Aug.,  1912.     The  linkage  of  two  factors  in  Drosophila  that 

are  not  sex-Hnked.     Biol.  Bull.,  23:  174-182. 
Morgan,  Sturtevant,  Muller,  and  Bridges.     Oct.,  1915.     The  mechanism  of    Men- 
deUan heredity.     Henry  Holt  &  Co.,  262  pp. 
Morgan,  T.  H.,  and  S.  C.  Tice.     Apr.,  1914.     The  influence  of  the  environment  on  the 

size  of  the  expected  classes.     Biol.  Bull.,  26:  213-220. 
Muller,  H.  J.,     Apr.,  May,  June,  July,  1916.     The  mechanism  of  crossing-over.     Am. 

Nat.,  50:  193-221,  284-305,  350-366,  421-434. 
Plough,  H.  H.     Nov.,  1917.     The  effect  of  temperature  on  crossing-over  in  Drosophila. 

J.  E.  Z.,  24:  147-209. 
Sturtevant,  A.  H.     Jan.,  1915.     The  hnear  arrangement  of  six  sex-hnked  factors  in 
Drosophila  as  shown  by  their  mode  of  association.     J.  E.  Z.,  14:  43-59. 

,  1915.     The  behavior  of  the  chromosomes  as  studied  through  Unkage.     Zeit.  f.  i. 

A.  u.  v.,  13:  234-287. 
Weinstein,  Alexander.     Mar.,  1918.     Coincidence  of  crossing-over  in  Drosophila  melan- 
ogaster  (ampelophila).     Genetics,  3:  135-172. 

304 


III. 


INHERITED  LINKAGE  VARIATIONS  IN  THE  SECOND 

CHROMOSOME. 


By  a.  H.  Sturtevant. 


305 


INHERITED  LINKAGE  VARIATIONS  IN  THE  SPX'OND 

CHROMOSOME. 


By  a.  H.  Sturtevant. 


INTRODUCTION. 

The  data  presented  in  this  paper  demonstrate  the  existence  of  two 
genes  that  influence  the  amount  of  crossing-over  in  the  second  chro- 
mosome of  Drosophila  inelanogaster  (ampelophila) .^  These  two  genes 
were  both  found  in  the  same  female,  that  came  from  a  stock  collected 
in  Nova  Scotia.  Each  of  the  genes,  in  females  heterozygous  for  it, 
decreases  the  amount  of  crossing-over  in  the  region  in  which  it  lies.  One 
of  them  (the  other  has  not  been  tested)  produces  no  appreciable 
effect  on  crossing-over  in  females  homozygous  for  it.  Those  results 
are  both  paralleled  by  the  effects  produced  on  the  third  chromosome 
by  a  gene  in  that  chromosome.  The  latter  case  is  discussed  briefly. 
An  account  is  also  given  of  a  race  in  which  the  amount  of  cnwNsing- 
over  in  one  region  of  the  second  chromosome  is  increased.  This  last 
case  is  not  yet  fully  worked  out. 

NOVA  SCOTIA  CHROMOSOME. 

The  two  loci,  vestigial  and  speck,  usually  show  about  37  per  cent 
of  crossing-over,  as  appears  from  the  summaries  here  presented  by 
Bridges  and  Morgan.  In  September  1913,  the  writer  mated  a  wild 
female,  of  a  fresh  stock  collected  by  Miss  E.  M.  Wallace  at  Livenxx)!, 
Nova  Scotia,  to  a  vestigial  speck  stock  that  had  been  used  in  ni:ikiiig 
the  crosses  reported  by  the  writer  (1915),  and  liad  in  those  crosses 
given  the  usual  result.  A  single  Fi  female  from  this  mating  w:us 
mated  back  to  three  vestigial  speck  males  of  the  above  stock  to  jiro- 
duce  culture  7  of  this  paper.  The  result  of  this  mating  was  55  wild- 
type  offspring  and  44  vestigial  specks — no  cross-overs  (see  .Vjipendix). 
Two  of  the  wild- type  daughters  were  mated  to  vestigial  speck  brothers, 
to  produce  cultures  68  and  69.  These  produced  2  cross-overs  among 
136  and  2  among  120  offspring,  respectively.  The  same  tyi^e  of  mat- 
ing was  repeated  in  the  next  generation,  in  cultures  104,  105.  106,  110, 
113,  and  114.  In  104  and  105  great  difficulty  was  cxperiencetl  in 
classifying  speck  (the  only  time  I  have  ever  noticed  such  a  difficulty 
with  this  character),  and  the  two  cultures  were  unfortunately  dis- 
carded without  any  attempt  being  made  to  see  wherein  the  difliculty 

'A  preliminary  note  on  this  case  has  already  been  published  (Sturtevant.  1917).     It  h»*  nlto 
been  discussed  by  Morgan,  Sturtevant.  Muller,  and  Bridges  (1015).  MuUcr  (191fi).  and  dwwher*. 

.  307 


308 


INHERITED   LINKAGE   VARIATIONS 


lay.  The  other  four  cultures  gave  again  few  or  no  cross-overs;  and 
this  type  of  mating  was  carried  on  for  two  additional  generations 
with  the  same  result  (see  Appendix).  It  is  evident  that  in  every  case 
the  tested  female  has  at  least  a  part  of  the  ''wild-type' '  second  chromo- 
some present  in  the  female  of  culture  7  and  derived  from  the  Nova 
Scotia  stock.  That  this  chromosome  is  really  responsible  for  the 
result  has  been  showTi  in  several  ways,  as  follows: 

A  wild-type  female  from  69  was  mated  to  4  black  curved  speck 
males  of  an  unrelated  stock.  The  Fi's  were  wild-type  and  speck  in 
approximately  equal  numbers,  as  would  be  expected.  Except  for  the 
rare  cross-overs,  all  the  not-speck  flies  should  have  carried  the  Nova 
Scotia  chromosome;  and  all  were  heterozygous  for  black,  curved,  and 
speck.  Two  such  wild-type  females  were  back-crossed  to  black 
curved  speck  males  (cultures  171  and  172).  They  gave  similar  re- 
sults, which,  when  added  show  the  following  relations : 


sp 


2 

-1 


419 


Total  440. 


20 


Here  we  have  the  same  reduction  of  curved  speck  crossing-over  that 
has  already  been  observed  for  vestigial  speck,  which  includes  the 
curved  speck  region,  and  also  a  reduction  of  the  black  curved  cross- 
ing-over. Experiments  exactly  analogous  to  these  have  been  carried 
out  with  curved  speck,  black  purple  vestigial  arc  speck,  black  purple 
curved,  star  black  purple  curved  speck,  black  purple  curved  morula, 
star  black  plexus,  and  other  stocks,  always  with  the  same  result — 
greatly  reduced  crossing-over  when  the  Nova  Scotia  chromosome  is 
present  (see  table  1).     In  several  of  these  cases  the  chromosome  in 

Table  1. — Tests  of  females  with  one  original  Nova  Scotia  chromosome. 


Loci. 


S'  b  Pr  c  Sp. 

S'bp^ 

b  pr  Vg  Or  Sp . 

b  PrC 

b  Pt  c  nif. . .  . 

b  c  Sp 

b  rrif . 

6  6a 

vg  Sp 

C  8p 


0 

1 

2 

3 

4 

1,2 

Total. 

222 

384 

1,083 

9,422 

2,108 

419 

272 

1,607 

1 ,  183 

1,171 

0 
0 
0 

26 
1 

20 

5 

104 

4 

1 

0 
12 
10 

82 
42 

1 

1 

0 

0 
0 
0 
3 

1 
0 

223 

396 

1,094 

9,533 

2,152 

440 

277 

1,711 

1,187 

1,172 

0 
0 
0 

1 
0 
0 

question  was  transmitted  through  males,  instead  of  females,  as  above,  | 
but  this  did  not  in  any  way  affect  the  result. 

Two  wild-type  females  from  110  were  mated  to  black  balloon  males] 
of  an  unrelated  stock.  All  the  offspring  were,  as  expected,  wild-typel 
in  appearance.  One  half  of  them  should  have  contained  the  "Novaj 
Scotia' '  chromosome,  the  other  half  should  have  received  the  vestigial] 
speck  chromosome,  and  therefore  should  have  given  the  usual  result! 


IN    THE    SECOND    CHROMOSOME. 


309 


Table  2. 


for  black  balloon  (48  per  cent).  12  of  these  females  were  back-crossed 
to  black  balloon  males,  and  gave  the  two  types  of  results  shown  in 
table  2. 

The  experiments  described  above 
demonstrated  that  the  unusual  result 
is  produced  when  the  Nova  Scotia 
chromosome  is  present;  the  black  bal- 
loon result  and  other  similar  ones  show- 
that  offspring  of  individuals  bearing 
such  a  chromosome  may  give  the  usual 
result,  these  evidently  being  the  off- 
spring that  do  not  receive  the  chromo- 
some in  question.  Table  1  shows  the 
results  obtained  from  females  bearing 
one  Nova  Scotia  chromosome. 

Since  there  is  here  a  total  of  only 
about  1.5  per  cent  crossing-over 
between  star  and  speck,  it  follows  that  we  have  almost  certainly  \)een 
dealing  throughout  with  a  second  chromosome  derived  entirely  (or 
at  least  all  of  it  between  star  and  speck)  from  the  original  Nova  Scotia 
stock. 

In  culture  193  a  female  heterozygous  for  curved  and  speck  and  for 
the  Nova  Scotia  chromosome  was  mated  to  a  curved  sixick  male. 
A  speck  female,  produced  as  the  result  of  crossing-over  between  curved 

Table  3. — Tests  of  females   with   one   Nova   Scotia   chromosome, 
the  speck  end  of  which  has  been  replaced. 


Culture. 

No.  of 

b  U 

No. 

OfTuprinR. 

rroiw-ovcri. 

p.  a. 

201 

131 

3  8 

2<);{ 

2o;{ 

7  9 

204 

201 

a  0 

206 

242 

fi.6 

207 

U.l 

3  4 

209 

ISO 

2.7 

210 

256 

5  9 

211 

347 

0.9 

202 

303 

41   3 

20.5 

38« 

54.1 

20S 

224 

44  6 

212 

402 

49 . 3 

Loci. 

0 

1 

2 

3 

4 

1.2 

TotaL 

b  Pr  Vg  Or  Sp 

b  Pr  c 

277 
478 
565 

0 
1 

7 

5 

6 

0 

0 

1 
0 

283 
485 
572 

b  3p 

and  speck  (and  therefore  bearing  the  original  Nova  Scotia  chromo- 
some, minus  its  speck  end) ,  was  mated  to  a  curved  male  of  stock.  Two 
daughters  of  the  latter  culture  (in  283  and  284)  gave  1  cross-over  be- 
tween curved  and  speck  in  505  offspring.  The  results  obtained  with 
this  Nova  Scotia  chromosome,  from  which  the  speck  end  liivd  been 
removed,  are  shown  in  table  3.  Evidently  the  speck  end  of  the  chromo- 
some is  not  responsible  for  the  unusual  results. 

As  will  be  shown  below,  the  Nova  Scotia  chromosome  was  ultimi\t4>ly 

i  separated  into  two  parts,  the  separation-point  being  betwwn  purple 
and  vestigial.  Tests  (see  table  16)  were  made  of  fenuiles  in  which 
both  parts  were  present,  but  were  each  united  to  parts  of  "normal" 

'chromosomes.  Culture  778  w^as  of  this  nature;  and  786  and  787 
contained  daughters  of  778  in  which  the  original  Nova  Scotiii  chromo- 


310 


INHERITED    LINKAGE    VARIATIONS 


some  had  been  reconstructed  by  crossing-over.  Table  4  presents  the 
results  from  these  two  cultures.  The  combined  data  from  tables  1, 
3,  and  4  are  summarized  in  table  5.  Figure  1,  second  line,  is  a  map 
based  on  this  table. 

Table  4. — Tests  of  females  with  one  reconstituted  Nova  Scotia  chromosome. 


0.0 


00 


Loci. 

0 

1 

2 

3 

Total. 

b  Pr  c  Sp 

549 

0 

6 

0 

555 

p- 


yg 


b 
— I — 

37.9         441  55.9 

S'b    pr  ■vgc  sp 


c 

— f— 
64.0 


sp 


94.2 


0.0    02   1.3  1.4 


0.0  0:5 

vgc  sp 
b  pr  .-.-• 

-\ +■■■ 


42.4      48  6  ■■; 


50.2  50.3 


y^ 


13.4  21.0 


t— 

0.0 


g'b    pr    c  sp 

06    0.'2    3:1  3.2 
S*.  b  pr 


T 


47.8 


0.0  0.3  0.4 


b     pr 
+      ■ 


sp 


38.2  41.7 


63.2 


I 


Fig.  1. — Maps  based  on  table  25.     The  first  corresponds  to  the  first  column  of  the  table, 

the  second  to  the  second  column,  etc. 

The  star  black  plexus  data  given  here  show  an  unexpectedly  high 
percentage  of  crossing-over  between  black  and  plexus.  The  data 
should  perhaps  not  have  been  included,  as  there  is  reason  to  believe 
that  another  gene  affecting  crossing-over  may  have  been  present  (see 
below,  p.  324).  For  this  reason  plexus  has  not  been  entered  on 
the  map  in  figure  1. 

The  black  balloon  percentage  (6.1)  is  unexpectedly  higher  than 
black  speck  (1.1).  As  may  be  seen  from  the  account  here  given  by 
Bridges  and  Morgan,  speck  and  balloon  certainly  give  less  than  1  per 
cent  crossing-over  in  ordinary  flies.  Unless  some  complication  is 
here  present,  balloon  must  be  to  the  right  of  speck,  and  the  speck 
balloon  region  must  give  more  crossing-over  than  usual  in  the  presence 
of  a  Nova  Scotia  chromosome. 


IN   THE    SECOND    CHROMOSOME. 


:^ii 


Table  6  shows  the  resuhs  obtained  from  second  broods,'  prcnluced 
by  feniales  containing  a  Nova  Scotia  chromosome.     TliescJ  data  were 

Table  5— Tests  of  all  females  bearing  one  Nova  Scotia  chromosome 

{region  from  star  almost  to  speck). 


Loci. 

0 

1 

Total. 

PercentaRC. 

S'b 

S'Pr 

S'  c 

S'Pz 

S'  Sp 

b  Pr 

b  Vg 

be 

619 

223 

221 

384 

222 

14,293 

1,362 

13,203 

384 

2,381 

3,117 

1,607 

1,362 

12,807 

2,109 

2,133 

2,560 

2,152 

2,892 

0 

0 

1 

12 

1 

33 

16 

185 

12 

48 

51 

104 

16 

141 

43 

23 

5 

0 

3 

619 

223 

223 

396 

223 

14,326 

1,378 

13,388 

396 

2,429 

3,168 

1,711 

1,378 

12,948 

2,152 

2,156 

2,565 

2,152 

2,895 

0  0 
0.0 
0  4 
3.0 
0  4 
0.2 
1.2 
1.4 
3.0 
2.0 
1.6 
6.1 
1.2 
1.1 
2.0 
11 
0  2 
0.0 
0.1 

ftp* 

b  ntf 

b  Sp 

660 

PrVg 

PrC 

Pr  "»r 

Pr  Sp 

Vg  Sp 

c  m^ 

C  Sp 

collected  in  order  to  find  out  if  there  is  a  change  in  the  linkage  value 
as  a  female  grows  older.  The  percentages  are  so  small,  however,  that 
a  comparison  with,  first  broods  can  give  no  significant  result.  The 
small  percentages  also  make  impossible  a  satisfactory  study  of 
coincidence  in  tables  1,  3,  and  4. 

Table  6. — One  original  Nova  Scotia  chromosome,  second  broods. 


Loci. 


S'b.. 
S'Pr. 
S'  c. 
S'  Sp. 
b  Pr.. 
be... 
b  nif. . 
b  Sp.  . 
Pr  C. 
Pr  rrir. 
Pr  Sp. 
c  rrif .  . 


0 

1 

Total. 

222 

0 

222 

221 

1 

222 

219 

3 

222 

219 

3 

222 

2,107 

9 

2,116 

2,084 

32 

2,116 

936 

12 

948 

219 

3 

222 

2,087 

29 

2,116 

937 

11 

948 

220 

9 

222 

948 

0 

948 

430 

0 

430 

Percentage. 


0.0 


0.9 
0.0 
0.0 


Culture  69,  referred  to  above  (p.  307),  contained  a  femiile  of  the 
Nova  Scotia^  ^^^^^  ^^  ^  ^,^  ^^  ^^^^     ^^^  vestiguil  male, 


constitution 


Vg  Sp 


produced  by  crossing-over  and  possessing,  presumably,  only  the  ex- 

'" First  brood"  and  "second  brood"  are  terms  applied  to  the  offsprinR  produced  when  a 
female  is  kept  in  one  bottle  for  9  or  10  days  (first  brood),  and  then  transferred  to  another  bottle 
for  a  second  period  of  9  or  10  days  (second  brood).  The  division  is  an  arbitrar>'  one.  and  doee 
not  correspond  to  any  "rhythm"  in  the  production  of  eggs. 


312 


INHERITED    LINKAGE    VARIATIONS 


treme  speck  end  of  the  Nova  Scotia  chromosome,  was  mated  to  a 
speck    female    of   stock.     The    not-speck    offspring    produced    were 

— - — ,  with  a  small  piece  of  the  Nova  Scotia  chromosome  opposite  s 


p. 


Four  females  of  this  constitution  were  tested,  in  cultures  166,  167, 
168,  and  169,  by  mating  to  vestigial  speck  males.  The  results  are 
shown  in  table  7. 

Table  7. 


Culture. 

0 

1 

Total. 

Sp              Vg 

-f-             Vg    Sp 

166 
167 
168 
169 

Total 

Percentaffe . . . 

85 
112 

48 
89 

60 
92 
62 
98 

46 
42 
46 
41 

24 
46 
30 
45 

215 
292 
186 
273 

334 
64C 

312 
1 

175       145 
320 

966 

33.1 

These  data  give  approximately  the  usual  value  for  vestigial  speck 
crossing-over,  and  therefore  agree  with  the  data  previously  presented 
in  indicating  that  there  is  no  effect  on  crossing-over  produced  by  the 
extreme  right-hand  end  of  the  Nova  Scotia  chromosome. 

TESTS  OF  CROSS-OVERS. 

When  the  earlier  experiments  with  the  Nova  Scotia  chromosome 
were  carried  out,  only  that  part  of  the  chromosome  from  black  to 
speck  or  balloon  was  studied.  Numerous  tests  of  cross-overs  were 
made,  in  order  to  find  out  what  part  of  the  Nova  Scotia  chromosome 
was  responsible  for  the  unusual  ratios.  The  result  obtained  was  that 
that  part  of  it  that  lies  to  the  left  of  a  point  between  purple  and  vestigial 
gave  approximately  the  ratios  found  in  ordinary  stocks;  but  that 
part  of  it  that  lies  to  the  right  of  this  point  between  purple  and  vestigial 
and  to  the  left  of  a  point  between  curved  and  speck  gave  what  seemed 
at  first  to  be  the  same  ratios  as  those  given  by  the  whole  Nova  Scotia 
chromosome.  It  was  therefore  concluded  that  the  peculiarity  was 
due  to  one  gene,  located  between  purple  and  speck.  But  it  soon 
appeared  that  this  right-hand  end  was  giving  a  little  more  crossing- 
over  in  the  black-curved  region  than  was  the  whole  Nova  Scotia 
chromosome.  By  this  time  star  had  become  available,  and  it  was 
now  found  that  star  and  black  gave  no  cross-overs  in  the  presence  of 
the  whole  chromosome,  but  gave  the  usual  40  per  cent  in  the  presence 
of  the  right-hand  end.  Tests  were  then  made  of  the  left-hand  end 
again,  and  star  and  black  were  found  to  give  no  cross-overs,  while 


IN   THE   SECOND    CHROMOSOME. 


313 


black-purple  gave  a  greatly  redaced  value.  It  therefore  follows  that 
the  original  Nova  Scotia  chromosome  contained  two  factors: 

Cn  I,  located  to  the  left  of  purple/  which  makes  star  black  0.0, 

and  reduces  black-purple. 
Ciir,  located  between  purple  and  speck/  which  greatly  reduces 
the  whole  purple  speck  region. 

RIGHT-HAND  END  OF  NOVA  SCOTIA  CHROMOSOME  {Cu ,). 
Culture  171  contained  a  female  with  an  original  Nova  Scotia  chromo- 

some  and  a  black  curved  speck  chromosome      "^      '^\  mated  to 

b    c     s„ 
8l  black  curved  speck  male.     It  is  included  in  tables   1  and  .').     A 
black  female,  produced  by  crossing-over,  must  have  had  the  right 

end  of  the  Nova  Scotia  chromosome,  but  not  the  left  (- —  "'  ] 

\h    c     sj 
This  female,  in  culture  226,  was  mated  to  stock  curved  speck  males, 
and  produced  146  offspring  without  a  cross-over  between  curved  and 

h    C 

speck.     A  wild-type  daughter,   ^ ,  was   mated   to  stock   blark 

c     Sp 

purple  curved  males   (culture  277)..     Among  105  offspring,  3  were 

cross-overs  between  black  and  curved.     One  of  the  three,  a  wild-type 

^  II  r 

daughter,  r ,  was   mated,    in    culture    318,    to    stock   black 

purple  curved  males.  Wild-type  daughters,  of  the  same  constitu- 
tion, were  again  mated  to  black  purple  curved  males  in  cultures  354 
and  355.    The  results  were  as  shown  in  table  8. 

Table  8. 


Culture. 

0 

1 

2 

1.  2 

Total. 

318 
354 
355 

Total 

Percentage .... 

227 
211 

184 

13 
11 
11 

3 

4 
2 

0 
0 
2 

243 
226 
199 

622 
93.1 

35 

5.2 

9 
1.3 

2 

668 

A  number  of  other  cultures  (see  table  9)  were  made  in  which  this 
same  right-hand  end  of  the  Nova  Scotia  chromosome  wa.^^  te^t<-d. 
All  were  descended  from  226,  277,  and  318.  The  results  are  included 
in  tables  10  and  11.  All  these  cultures  agreed  in  showing  that  for 
the  purple-to-speck  region  we  have  a  result  not  very  different  from 
that  given  by  the  whole  Nova  Scotia  chromosome;  but  for  the  bUick 
purple  region  the  result  is  not  very  different  from  the  usual  one. 

'  Tests  made  more  recently,  in  connection  with  studies  of  Cm,  it  («ec  l)elow).  indicat«  th*t 
Cui  ia  probably  to  the  left  of  black,  and  that  C//r  is  certainly  to  the  left  of  plexu«. 


314 


INHERITED    LINKAGE    VARIATIONS 


Numerous  other  tests  have  been  made  of  the  right  end  of  the  Nova 
Scotia  chromosome.  Table  9  gives  a  hst  of  the  different  cross-overs 
tested,  together  with  the  cultures  derived  from  those  sources.  In 
addition,  there  are  a  number  of  cultures  (including  all  those  in  which 
the  character  star  was  tested)  in  which  the  origin  of  the  Cn  r  segment 
is  uncertain,  because  it  has  been  passed  through  females  homozygous 
for  Cji,  from  different  sources  (see  below). 

Table  9. — Tests  of  right-hand  end  of  Nova  Scotia  chromosome. 


Culture  in 

which  cross-over 

occurred. 

Loci  between 

which  cross-over 

occurred. 

Cultures  representing  this  piece  of 

the  Nova  Scotia  chromosome 

(see  Appendix) . 

171 

524  V 
524  V 
685 

be 

Vr  Vn 

226,  277,  318,  351,  352,  353,  354, 
355,  377,  379,  380,  404,  416,  417, 
430,    431,    432,    433,    446,    448, 
449,    450,    467,    468,    469,    470, 
471,    472,    473,   480,   495,   496, 
500,  511,  512,  513,  517 

547 

545,  546,  569,  622,  686,  687,  719, 

721,  723,  724,  725,  763 
707,  708,  709 

Vt  C 

These  cultures  all  contain  only  that  part  of  the  Nova  Scotia  chromo- 
some that  lies  to  the  right  of  a  point  between  black  and  curved  (171 
series),  purple  and  vestigial  (two  524  N  series),  or  purple  and  curved 
(685  series).  Since  they  all  agree  in  the  results  produced,  we  may 
conclude  that  the  gene  responsible  for  these  results  is  located  some- 
where to  the  right  of  purple.  In  deaUng  with  the  original  Nova 
Scotia  chromosome  we  found  that  removal  of  the  speck  end  made  no 
difference  in  the  ratios  given.  It  was  therefore  to  be  expected  that 
the  right-hand  piece  would  show  the  same  relation,  {.  e.,  that  Cur 
is  between  purple  and  speck.  The  following  data  show  that  such  is, 
in  fact,  the  case. 

Culture  546,  of  the  second  524  N  series,  contained  a  female  of  the 


constitution 


h   Vr        C 


II  r 


dr    Sp 


mated   to  black  purple  arc  speck  males. 


By  double  crossing-over,  a  female  was  produced  of  the  constitution 

Pr     Cjjr    Sp 


Vr       «r 


This  female,  in  which  the  extreme  speck  end  of  the 


old  Nova  Scotia  chromosome  had  been  lost,  was  mated  to  black  purple 
vestigial  arc  speck  males,  in  culture  570.  All  later  cultures  of  the 
second  524  N  series  received  their  Cj/ ,  from  this  female.  They  gave 
essentially  the  same  results  as  the  other  Cj/r  cultures,  and  have 
therefore  been  included  in  tables  10  and  11.  The  fourth  line  of 
figure  1  represents  a  map  based  on  table  1 1 . 


IN    THE    SECOND    CHROMOSOME. 


31n 


Table  10. — C 

7/r. 

Loci. 

0 

1 

2 

3 

4 

1,2 

1,3 

2,3 

2,4 

3,4 

1.2,3 

Toul. 

S'  b  pr  c  8p 

805 
420 
198 
101 
700 
943 
7,009 
888 
578 
141 
790 
690 
609 
146 

435 
163 
830 
234 
217 

657 

297 

10 

16 

39 

59 

427 

86 

25 

15 

65 

44 

6 

0 

292 

139 

70 

50 

5 

86 

26 

2 

0 

26 

12 

103 

61 

17 
10 
0 
0 
0 
0 

1 
0 

32 
9 
0 
0 
0 
1 
10 
11 

11 
3 
0 
0 
0 
0 

2 
2 

0 
0 
0 
0 

1 

1 

2 
0 
0 
0 
0 
0 

1,015 

707 

210 

117 

7fW 

1,015 

7.54B 

1,040 

003 

150 

K55 

7:i4 

61.'. 

140 

794 
320 
92.1 
323 
222 

S'  b  Pr  8n 

b  Vt  Vn  CLt  8n 

0 

0 

b  Pr  Vg  Sp 

b  Pf  c   irif 

b  Pr  c  Sp 

b  PrC 

b  PrSp 

b  Pf 

b   Vg  Sp 

0 

0 

be 

6  rrir 

Pr  c 

C  Sp 

Second  broods. 
S'  b  Pr  C  Sn 

32 
11 

20 

35 

0 

16 
2 

0 

9 
3 
3 
4 
0 

5 
2 

3 
0 

0 

0 

2 
0 

S'  b  Pr  Sp 

b  Pr  c 

.... 

b  Pr  Sp 

. . . . 

. . .  . 

b  Vg  Sp 

. . . . 

•    •   <    > 

Table  11.— C//, 

Loci. 

0 

1 

T. 

Percentage. 

Loci. 

0 

1 

T. 

Pcrccnt4Mf«*. 

S'b.... 

1,371 

1,011 

2,382 

42.4 

'   Second 

S'Pr... 

1,275 

1,107 

2,382 

46.5 

broods. 

S'  c... 

851 

764 

1,615 

47.3 

S'b.... 

662 

452 

1,114 

40  6 

S'  Sp... 

852 

763 

1,615 

47.2 

1  S'Pr... 

630 

484 

1,114 

43  5 

b  Pr 

12,843 

844 

13,687 

6.2 

i  S'c... 

452 

342 

794 

43  0 

bvg 

440 

43 

483 

8.9 

,  S'  Sp... 

452 

342 

794 

43  0 

be 

10,920. 

879 

11,799 

7.4 

bpr.... 

2,390 

192 

2,582 

7  4 

b  rrir- .  ■  . 

1,390 

109 

1,499 

7.3 

.    b  Vg. .   .   . 

217 

5 

•)'>0 

2  3 

b  Sp.  .  .  . 

4,470 

456 

4,926 

9.2 

be 

1,502 

155 

1,717 

9   1 

PrVg.... 

325 

2 

327 

0.6 

b  Sp... . 

1,498 

161 

1,6.59 

9  7 

PrC 

11,368 

191 

11,559 

1.6 

PrC 

1,668 

49 

1,717 

2  9 

Prmr..  . 

739 

26 

765 

3.4 

Pr  »p-  ■■ 

1,370 

67 

1,4.37 

4  7 

Pt  Sp.  .  . 

4,6.34 

136 

4,770 

2.9 

Vg  Sp.   .. 

'>•>•> 

0 

•j-ft 

0  0 

Vg     Sp..  . 

483 

0 

483 

0.0 

C  Sp. . . . 

794 

0 

794 

0  0 

C  TJlr.  .  . 

765 

0 

765 

0.0 

C    Sp 

2,773 

3 

2,776 

0.1 

The  second-brood  data  are  not  ver>'  conchisivo.  Star-blark  is 
perhaps  lower  than  in  first  broods;  but  the  black  ]>urj)le  ourvod  com- 
binations, for  which  there  is  more  adequate  data,  all  ;iive  a  slight  in- 
crease. As  is  shown  by  the  data  presented  by  Plough  (1917),  more 
exact  methods  are  needed  in  studying  this  problem.  An  exj)orimont 
with  Ciir  is  now  planned  in  which  the  females  will  be  transferred 
every  two  days.  Until  data  from  such  an  experiment  are  avaihible 
further  discussion  would  be  out  of  place. 


316 


INHERITED    LINKAGE    VARIATIONS 


LEFT-HAND  END  OF  NOVA  SCOTIA  CHROMOSOME  {Cm). 

Culture  678  was  derived  from  a  female  with  an  original  Nova  Scotia 
chromosome  and  with  black,  purple,  curved,  and  morula  in  its  mate, 
mated  to  four  black  purple  curved  males.  The  culture  is  included 
in  the  totals  given  in  table  1.  It  produced  three  curved  flies  by  cross- 
ing-over. These  flies  must  have  had  the  left-hand  end  of  the  Nova 
Scotia  chromosome,  up  to  a  point  between  purple  and  curved;  but 
the  right-hand  end  of  the  Nova  Scotia  chromosome  had  been  lost. 
One  of  them,  a  male,  was  mated  to  a  black  purple  female  that  had 
the  right-hand  end  of  the  Nova  Scotia  chromosome  {Cur)-  A  wild- 
type  daughter  was  mated  to  black  purple  curved  morula,  and  gave 
results  that  ydW  be  discussed  below  (see  table  16).  A  curved-morula 
son,  that  must  again  have  had  the  left-hand  end  of  the  Nova  Scotia 
chromosome,  was  mated  to  a  similar  black  purple  female ;  and  a  wild- 
type  daughter  was  once  more  back-crossed  to  black  purple  curved 
morula  in  culture  752.  This  time,  however,  it  was  decided  to  get  the 
influence  of  the  left-hand  piece  of  the  Nova  Scotia  chromosome  with- 
out the  presence  of  the  right-hand  end.  A  curved  morula  male  from 
752  was  accordingly  mated  to  a  star  black  female  of  an  unrelated 

S'     h 

stock.    A  daughter,  of  the  constitution  ^ ,  with  the  end  of 

L///    c    rrir 

the  Nova  Scotia  chromosome  opposite  star  and  black,  was  mated  to 

black  purple  curved  speck  males,  in  culture  776.    The  result  was  106 

non-cross-overs,  0  cross-overs  between  star  and  black,  and  38  cross-overs 

between  black  and  curved.     Further  tests  with  descendants  of  776,  in 

which  the  same  piece  of  the  Nova  Scotia  chromosome  was  present,  gave 

the  results  shown  in  table  12  (culture  776  itself  is  included). 


Table 

12.- 

-Ciie 

Loci. 

0 

1 

2 

3 

1,2 

0 
0 
0 

1 

0 
0 
0 

2,3 
141 

41 
6 

T. 

*S'bcsp... 

S'bc 

b  p,  c  Sp..  . 
bprSp 

Second 
broods. 

*S'  bcsp... 

S'bc 

b  Pr  c  8p.. . 

1,006 

200 

91 

138 

576 

96 

137 

0 
0 
0 
1 

0 
0 

0 

455 

54 

35 

109 

216 
11 
36 

649 

"es" 

337 

82" 

2,251 
254 
200 
249 

1,170 
107 
261 

*  Done  with  H.  H.  Plough,  and  already  reported  by  him  (Plough,  1917). 

Clearly  we  have  here  the  same  results  for  star  purple  as  in  the  case 
of  the  original  Nova  Scotia  chromosome ;  but  for  purple  speck  we  have 
nearly  the  usual  result.  r*        n 

.  ^  II  t        ^  II  r 

Culture  259  contained  a  female  of  the  constitution  7 

b      Pr      Vg      ttr     Sp 

(original  Nova  Scotia  chromosome),  and  two  stock  b  Pr  Vg  a^  Sp  males. 


IN   THE    SECOND    CHROMOSOME. 


317 


One  vestigial  (arc)  speck  male  was  produrod  by  crossinR-ovcr.     He 
must  have  had  the  left-hand  end  only  of  the  Nova  Scotia  chromcv 

Cjll  Vg  ttr  Sp 

He  was  mated  to  a  hliick  female  of  stock, 


some, 


6      Pr      Vg      ttr      Sp 


and  two  wild-type  daughters, 


Cm    Vg    a,    .«? 


,  were  tested,  in  cultures 


328  and  329.     They  gave  the  results  shown  in  table  13. 

Table  13. 


Culture. 

0 

1 

2 

1.  2 

TotAl. 

Vg     Sp 

b 

+ 

bv^  ip 

Vg 

b    p 

«p 

6  Vg 

328 
329 

Total 

Per  cent.  . 

77 
44 

75 
40 

28 
13 

5 

7 

79 
31 

63 
43 

8 
2 

6 
1 

341 
181 

121 

115 

41 

12 

110 

106 

10 

7 

522 

236 

53 

216 

17 

45.2 

10.2 

41.4 

3.3 

These  data  have  been  added  to  those  of  table  12  in  the  summary 
for  Cm,  table  14.  The  corresponding  map  is  shown  in  the  third  line 
of  figure  1. 

Table  14. — Cur,  summary. 


Loci. 


S'  b.. 
S'  c. 
S'sp. 
b  Pr. 

b  Vg.  . 

be.  . 

6  8p.  . 
PfC. 

PrSp. 

Vg  8p. 
C  Sp.. 


Second  broods. 


S'b.. 
S'  c. 
S'sp. 
bpr. 
be. 
b  Sp. 
PrC 
PrSp. 
C  Sp.  . 


0 


2,505 

1,855 

1,147 

447 

452 

2,014 

1,497 

159 

236 

289 

1,587 


1,277 
1,009 
617 
261 
1,228 
760 
219 
143 
905 


1 


0 

650 

1,104 

2 

70 

691 

1,476 

41 
213 
233 
864 


0 

268 
553 
0 
310 
671 
42 

lis 

466 


Total. 


2,505 

2,505 

2,251 

449 

522 

2,705 

2,973 

200 

449 

522 

2,451 


1,277 

1,277 

1,170 

261 

1,538 

1,431 

261 

261 

1.431 


Percentage. 


0  0 
25.9 
49.0 

0.5 
13.4 
25.4 
49.7 
20.5 
47.4 
44  6 
35.3 


0.0 
21.0 
47.3 

0  0 
20  1 
47.0 
10.1 
45  2 
32.6 


The  values  obtained  from  second  broods  (table  14)  run  consi.'^tontly 
a  trifle  lower  than  the  corresponding  values  for  first  broods.  The 
differences  are  small  in  every  case;  but  since  all  are  in  the  .s:imo  direc- 
tion, and  since  females  with  neither  Cm  or  C;/ .  show  an  age  clumge 


318 


INHERITED    LINKAGE    VARIATIONS 


in  this  same  direction  (Bridges,  1915;  Plough,  1917),  the  decrease  is 
probably  significant.  More  exact  methods  (see  Plough,  1917)  are 
necessary  for  obtaining  clear-cut  data  on  this  point,  as  has  already 
been  stated. 

Here,  as  also  in  the  case  of  C//,,  wherever  reliable  information 
regarding  coincidence  is  available,  the  value  is  not  far  from  the  one 
found  in  females    that   contain   neither  Qm  nor  C//,.  (see   Bridges 

Cm 


Table  15. 


Cii, 


Loci. 

S'  b  Pr  c  Sp 

b  PtC 

b  Pt  c  mr 

Second  cultures 

S'  b  Pr  c  Sp  . 


0 

1 

2 

3 

4 

1,2 

Total. 

659 

0 

1 

24 

1 

0 

685 

226 

2 

10 

,    , 

0 

238 

631 

0 

12 

0 

643 

497 

0 

0 

11 

1 

0 

509 

Table  16. — 


Cn 


Cllr 


Loci. 

0 

1 

T. 

Percentage. 

S'  b           

685 

684 

660 

659 

1,563 

1,517 

631 

659 

1,520 

631 

660 

643 

684 

509 
509 
498 
497 
509 
498 
497 
498 
497 
508 

0 

1 

25 

26 

3 

49 

12 

26 

46 

12 

25 

0 

1 

0 

0 
11 
12 

0 
11 
12 
11 
12 

1 

685 

685 

685 

685 

1,566 

1,566 

643 

685 

1,566 

643 

685 

643 

685 

509 
509 
509 
509 
509 
509 
509 
509 
509 
509 

0.0 
0.1 
3.6 
3.7 
0.2 
3.1 
1.9 
3.7 
2.9 
1.9 
3.6 
0.0 
0.1 

0.0 
0.0 
2.2 
2.4 
0.0 
2.2 
2.4 
2.2 
2.4 
0.2 

S'  Pr 

S'  c 

S'  Pr 

h    V-r 

be 

b  rrir 

b  Sn 

■n-  c     

Dr  17I9 

7)-    Sn 

C  Sp 

Second  broods. 
S'  b 

S'  Pr 

S'  c 

S'  Sj, 

5  T)* 

6  c 

h  Sp 

7)r  C           .                

7)^  St*                             

C  Sn 

and  Morgan,  1919).  But  in  no  case  does  this  include  a  region  in  the 
"sphere  of  influence"  of  the  cross-over  gene  present;  for  in  all  such 
regions  the  percentage  of  crossing-over  is  too  small  to  give  statistically 

reliable  results. 

Cii  I 


Cii, 


Pr 


Cultures  677  and  678  both  contained  females,   7^ 7^ —  (678  was 

also  heterozygous  for  m,),  mated  to  6  p^  c  males.    A  cross-over  female, 


IN   THE    SECOND   CHROMOSOME.  319 

0       Pr       Cjir        .  „__  ,       ,  Cut        C       m 

7 — - — - —  ,  from  677  was  mated  to  a  cross-over  male,  t-^^-^ ' 

^    Pt    ^  '  b    p,   c 

from  678.     The  resulting  wild-type  offspring  were  r^ — —.     A 

"       Pr         Cjjr 

female  of  this  constitution,  in  culture  718,gave4..3  per  cent  crossinK-ovor 
between  pr  and  c,  none  between  6  and  yr  or  between  c  and  vxr.    The 

same  general  method  was  followed  in  making  up  seven  other     "^  , — 

^    ttr 

females.  The  same  Cm  c  chromosome  was  present  in  all  these 
females,  but  Cii  r  from  different  sources  was  used.  The  results  from 
these  females  are  given  in  tables  15  and  10  and  the  fifth  line  of  figure  1. 
These  data  agree  with  those  obtained  from  Cm  C'//,,  except 
that  Pr  c  shows  a  slight  rise  (from  1.1  to  2.9).  Owing  to  the  statistical 
difficulty  of  handling  such  small  ratios  it  is  not  possible  to  say  whether 
this  difference  is  significant  or  not  until  more  data  can  be  collected. 
The  point  is  of  interest  in  its  bearing  on  the  mechanism  of  the  action 
of  Cm  and  Cur,  but  must  be  left  unanswered  for  the  present. 

The  second  brood  data  here  presented  for    -^^ are  entirelv 

Cllr 

inadequate  for  the  purpose  of  detailed  comparison  with  first  brocxis. 
They  do,  however,  show  an  increase  for  pr  c  over  the  Cm  C^r 
second  broods  (from  1.2  to  2.2). 

HOMOZYGOUS  dir. 

We  have  seen  that  heterozygous  C^r  greatly  decreases  crossing- 
over  in  the  region  from  purple  to  speck,  but  does  not  ai^preciiibly 
affect  the  region  from  star  to  purple.  The  data  now  to  be  presented 
show  that  homozygous  Cjir  gives  a  value  for  purple  speck  that  is 
very  close  to  that  found  in  "normal' '  flies,  but  again  does  not  influence 
the  region  from  star  to  purple. 

It  has  so  far  not  been  found  possible  to  obtain  a  chromosome  con- 
taining Cii  r  with  vestigial  or  curved,  since  heterozygous  ('/; ,  practi- 
cally prevents  all  crossing-over  in  the  region  in  which  these  three  genes 
are  located.  For  this  reason  none  of  the  data  on  homozygous  Cn  r 
deal  with  loci  between  purple  and  speck. 

HOMOZYGOUS  C//.  WITH  Cm. 
In  the  course  of  the  experiments  with  Cur  a  chromosome  of  the 
constitution  ♦S'  h  pr  Cnr  Sp  was  obtained.^     When  males  with  this 

Pr  O/  r  *p 

1  This  chromosome  was  derived  from  culture  570  (see  p.314).  in  which  was  a  fcmalo  ^  ^      Or    *p' 

A  cross-over  in  this  female  gave  a  6  Pr  Cn  r  «p  chromosome.  This  chromosome,  or  a  dcriv»uve 
of  it,  since  it  had  perhaps  been  passed  through  a  b    ;,^    c'nl   »     ^^'"'^'^'  ^'^  '''""^  oppo«t«  •t«r 

(  — )  in  the  females  of  cultures  G9G  and  099a.     The  chromosome  rofcrrcd  to  a»x>v« 

\    0  Pr  tn  T  Sp  /  ■  I.         t 

(5'  h  Pr  Cn  r  Sp)  was  produced  by  crossing-over  in  these  females  and  was  kept  inUct  thcns»ft4sr 
by  breeding  from  males  heterozygous  for  it.  in  which  no  croaaing-over  occurred. 


320 


INHERITED    LINKAGE   VARIATIONS 


C 


III 


'II  r 


chromosome  were  mated  to  females  of  the  constitution 

0    Pr    c  ' 

the  star  not-black  offspring  must  have  been  of  the  constitution 
— z^ — y^ — -.    Nine    such  females  were    tested  by  mating   to 

^11 1  ^Ilr 

h  Pr  Sp  males  and  gave  the  results  shown  in  the  first  line  of  table  17. 
The  data  in  the  second  row  were  obtained  in  the  same  way,  except 
that  no  star  had  been  put  in  the  h  Pr  Cn  r  Sp  chromosome.  The  third 
line  represents  the  offspring  of  a  female  (culture  340)  of  the  constitu- 


tion 


III      iir  ^^  produced  by  mating  a  male        ^ 


h     C 


to  a  female 


II  r 


b         Cur 

^^ — -.    The  males  in  340  were  black  purple  vestigial  arc 

speck;  since  no  purples  were  produced  the  female  must  have  received 
a  6  CjiT  chromosome  from  her  father;  and  since  she  gave  45.2  per 
cent  crossing-over  between  black  and  speck,  instead  of  the  9.0  char- 
acteristic of  Cii  r  females,  she  must  have  received  from  her  mother 

^11   I     ClI  T     8p' 

Cii  I    Cii  r 


Table  17.— 


Cllr 


Loci. 

0 

1 

2 

3 

1,2 

1,3 

2,3 

1,2,3 

Total. 

.S'  b  Pr  Sp.  .  . 

b  PrSp 

b  Sp 

1,047 
154 
144 

3 

0 

119 

0 
138 

942 

0 

1 

1 

0 

2 

1,995 
293 
263 

Table  18.— 


Cm    Ciir 

Cllr 


Loci. 

0 

1 

Total. 

Percentage. 

S'h.... 

1,989 

61 

1,995 

10.3 

S'  Pr.-. 

1,989 

61 

1,995 

10.3 

S'  Sp... 

1,048 

947 

»1,995 

47.5 

b  Pr.  .  . 

2,285 

3 

2,288 

0.1 

b  Sp. . . . 

1,351 

1,200 

2,551 

47.0 

PrSp.  .. 

1,204 

1,084 

2,288 

47.4 

1  These  cross-overs  are  very  doubtful.  None  of  them  were  tested;  and  there  is  a  small  per- 
centage of  error  in  classifiying  star  flies.  Similar  apparent  cross-overs  were  obtained  in  working 
with  C,f  (,  but  all  were  shown,  when  tested  to  see  if  star  was  really  present  or  not,  to  be 
wrongly  classified. 

Table  18  and  the  sixth  map  of  figure  1  summarize  the  data  from 
these  three  series  of  experiments.  No  second-brood  data  are  avail- 
able ;  and  the  star  to  purple  region  gives  so  few  cross-overs  that  coinci- 
dence can  not  profitably  be  studied.  It  is,  however,  very  remarkable 
that  all  three  cross-overs  between  black  and  purple  were  also  cross- 
overs between  purple  and  speck.  More  data  is  needed  before  we  can 
be  sure  this  is  a  significant  result,  since  purple  and  speck  themselves 
cross  over  so  frequently  (47.4  per  cent). 


IN   THE   SECOND   CHROMOSOME. 


821 


Comparison  of  table  18  with  table  14  will  show  tlmt  tlic  n>MiItH 
C       C 
given  by  ;^  and  by  Cjji  arc  almost  if  not  (luite   the  Kiiine. 


C 


11  r 


That  is,  homozygous  Cn ,  gives  the  same  result  as  no  Cu ,. 

HOMOZYGOUS  C/y  .-WITHOUT  Cji ,. 
b  Pr    Ctt 


A  female 


b  Pr   cm 
was  mated  to  a  male 
see   above. 


Jli lLi.\ 

h    p,    c    rrirj 


Clir      s 


(a  cross-over  from  G99,  q.  v., 


U      Pr      tjir      Sp 

Six   wild-type  daughters   were    tested    by    milling    to 

b  Pr  c  Sp  males.    Four  gave  the  expected  result  for  —^ •'  females ; 

and  two  (745  and  748)  gave  no  curved  offspring,  so  that  they  must 
have  been  r 7^ — - — - . 

b    Pr   Ciir 

Females  885  to  888   contained  a  *S'  6   Cn  r  chromosome  dorivod 
from  the  pr~^  experiments  and  a  Pr  Cur  s„  chromosome  derived 

from  a  stock  culture  that  came  from  culture  570  {q.  r.,  p.  314).  It  is 
quite  possible  that  some  or  all  of  these  females  carried  another  gene 
affecting  crossing-over   (Cju,  u — see  below) ;  but  the    results    have 

Cllr 


Table  19.— 


C 


II  r 


Loci. 

0 

1 

2 

3 

1,2 

1.3 

2.3 

1.2.3 

Total. 

b  PrSp 

b  Sp 

S'  b  Vt  Sp^  ■  ■ 

295 

77 
303 

9 

74 

192 

161 

6 

471 
151 
917 

16 

242 

2 

156 

12 

4 

Table  20. 


Loci. 

0 

1 

Total. 

PercentaRe. 

S'b 

S'Pr 

S'  Sp 

b  Pr 

h  8p 

Pr  Sp 

573 
551 
473 
1,349 
851 
817 

354 

376 

454 

49 

698 
581 

927 

927 

927 

1,398 

1,.549 

1,398 

38.2 
40,6 
49.0 
3.5 
45.0 
41.5 

been  included  because  they  are  the  only  ones  available  for  S'  in  the 
presence  of  homozygous  Cu  r-  Other  work  done  with  Cm,  u  makes  it 
probable  that  this  gene  would  not  seriously  affect  any  region  except 
that  from  purple  to  curved;  and  the  purple  speck  values  for  this 
experiment  agree  with  those  from  745  and  74S.  TluTcfore  the  two 
results  are  probably  comparable.  Both  are  inclucknl  in  tables  19  and 
20  and  the  last  line  of  figure  1. 

'May  contain  Cni,  //• 


322  INHERITED    LINKAGE    VARIATIONS 

For  this  combination  also  no  second-brood  data  is  available.     Coinci- 
dence seems  to  be  of  approximately  the  value  that  is  usual,  but  can 
be  satisfactorily  studied  only  in  the  series  that  may  have  Cm,  n- 
(J 

The  7^  ratios  are  clearly  not  very  different  from  those  obtained 

with  the  "usual' '  second  chromosome. 

NO  TESTS  OF  HOMOZYGOUS  Cm. 

No  tests  were  made  of  females  homozygous  for  Cm,  because  it 
was  hoped  that  a  cross-over  would  occur  that  would  give  a  *S'  Cm 
chromosome,  and  thus  make  possible  a  test  of  the  region  in  which 
Cm  is  located.  A  few  attempts  were,  it  is  true,  made  to  get  a  pure 
stock  of  Cm',  but  no  careful  records  were  kept,  and  these  attempts 
were  all  unsuccessful.  Recent  tests  show  that  there  is  now  a  lethal 
gene  in  the  Cm  chromosome  that  is  being  studied,  so  that  it  will 
probably  be  impossible  to  obtain  homozygous  Cni-  It  is  not  certain 
whether  this  lethal  represents  a  recent  mutation  or  not. 

TESTS  SHOWING  NO  CROSSING-OVER  IN  MALES. 

Very  few  counts  have  been  made  from  heterozygous  males;  but  no 
crossing-over  in  males  has  been  assumed  throughout  the  work,  and 
has  been  depended  on  frequently  in  keeping  stocks  and  in  producing 
many  of  the  more  unusual  combinations  of  Cm  and  Cnr.  These 
matings  have  never  produced  flies  that  seemed  to  result  from  crossing- 
over  in  males,  and  have  always  given  in  later  generations  results  that 
are  consistent  with  the  view  that  such  crossing-over  does  not  occur. 
Taking  this  evidence  in  connection  with  the  counts  given  below 
(table  21),  and  with  the  evidence  that  shows  crossing-over  not  to 
occur  in  males  of  Drosophila  in  any  of  the  chromosomes  under  any 
known  circumstances/  we  may  safely  conclude  tnat  Cni  and  Cur 
do  not  cause  exceptions  to  the  general  rule. 

CONSTITUTION  OF  THE  NOVA  SCOTIA  STOCK. 

The  original  Nova  Scotia  female  had  in  her  second  chromosome  two 
factors  for  decreased  crossing-over.  It  would  be  of  some  interest  to 
find  out  whether  or  not  this  condition  was  widespread  in  the  stock  from 
which  she  came.  Unfortunately  the  original  stock  was  lost  before  it 
was  discovered  that  two  factors,  instead  of  one,  are  responsible  for 
the  result.  The  following  tests  are  therefore  not  entirely  satisfactory. 
Three  females,  from  the  Nova  Scotia  stock,  were  mated  to  curved 
speck,  and  4,  4,  and  1  daughters,  respectively,  were  back-crossed  to 
curved  speck.  Only  a  few  offspring  were  counted  from  each,  but 
enough  to  show  that  all  9  females  were  giving  at  least  20  per  cent  of 

'  Except  the  curious  case  of  "somatic  crossing-over"  recorded  by  Muller  (1916). 


IN   THE    SECOND   CHROMOSOME. 


82:^ 


crossing-over.  It  follows  that  Cn ,  was  not  present.  Three  females 
from  Nova  Scotia  stock  were  crossed  to  black  vestiKiiil,  and  diiii^hters 
Table  21. — Tests  for  crossing-over  in  males. 


Culture. 

Crossover 

constitution. 

Mutant 
genes. 

Non- 
cro.'w-overs. 

CroM- 
overa. 

Total. 

108 
109 

621 

CiiiCiir 
Cut  CiiT 

Vg    Sp 
Vg    8p 

37 
61 

49 
52 

0 
0 

MI 
113 

98 

101 

0 

199 

Cur 
Cur 

b 

PrSp 

2 

7 

0 

9 

624 
33Sa 

Cur 
Cii  r 

Cii  I  Cii  r 
Cii  t 

b 

Sp 

b 

Sp 

6 

5 

0 

11 

8 

12 

0 

20 

5 

8 

0 

13 

338& 

Cii  I  Cii  , 

Cii  r 

b 

Sp 

58 

58 

0 

116 

423 

Cii  I  Cii  r 
Cur 

b  Sp 

143 

146 

0 

289 

424 
741a 

Cii  I  Cii  r 
Cur 

Cii  t  Cii  r 
Cur 

b  Sp 
S'  Sp 

81 

77 

0 

158 

287 

289 

0 

576 

108 

112 

0 

220 

7416 

Cii  I  Cit  r 

Cii  r 

S'  Sp 

So 

87 

0 

172 

193 

919 

0 

392 

718 

Cii  r.  or 

Cur 
Cur 

S' 

Sp 

88 

102 

0 

190 

Table  22. 


Mother. 

Culture. 

b  vg 
percentage. 

No.  of 
offspring. 

N 

230 

8.5 

25'* 

N 

231 

9.6 

270 

A^ 

232 

10.7 

140 

V 

233 

13.9 

202 

V 

234 

11.9 

168 

V 

235 

16.2 

191 

V 

236 

12.9 

295 

V 

237 

13.7 

2t>9 

V 

238 

20.0 

135 

B 

239 

12.3 

235 

B 

240 

23.0 

161 

324  INHERITED    LINKAGE    VARIATIONS 

were  back-crossed  to  black  vestigial  (cultures  230  to  240  inclusive). 
The  results  are  shown  in  table  22. 

None  of  these  females  had  both  Cm  and  Cun  but  it  is  possible 
that  one  of  the  factors  may  have  been  present,  especially  in  the  off- 
spring of  female  N.  These  tests  show  only  that  the  Nova  Scotia 
stock  was  not  homozygous  for  Cjj  „  and  probably  not  for  Cn  i.  No 
other  stocks  from  northern  localities  have  been  tested,  so  that  it  is 
impossible  to  even  guess  whether  or  not  these  factors  occur  frequently 
in  Nova  Scotia  or  neighboring  regions. 

ANOTHER  SECOND-CHROMOSOME  LINKAGE  VARIATION. 
Cultures  733  and   734,   referred   to   elsewhere,    contained  females 
of  the  constitution   ^7 — r .     As  was   pointed    out   above,    they 

gave  an  unexpectedly  high  percentage  of  crossing-over  for  black  and 

plexus.     Culture  812,   descended  from  the  same  culture  that  pro- 

*S    b  7)     c  s 
duced  females  733  and  734,  contained  a  female  y^ ^   ^ .    This 

^IIl  ^Ilr 

female  produced  72  offspring,  of  which  none  were  cross-overs  between 

S'  and  Pr,  or  between  c  and  Sp,  but  11  were  cross-overs  between  p, 

C       C 

and  c.     Later  descendants  of    812,  of    the    constitution  £ -, 

0    pr     c  ' 

gave  this  same  increased  value  for  p^  c  without  any  increase  for  b  p^. 
But  it  was  found  impossible  to  fix  this  increased  value,  which  fluctu- 
ated between  the  expected  value  (less  than  1  per  cent)  and  20  to  30 
per  cent.  Several  selection  experiments  have  been  carried  out  in  an 
effort  to  get  a  stock  that  would  constantly  give  the  high  value,  but 
without  success.  The  most  recent  of  these  experiments  has  now  been 
carried  through  23  generations  of  brother-sister  matings,  always 
breeding  only  from  those  pairs  that  gave  the  ''high"  value  for  p^  c. 
Yet,  in  the  fifteenth  generation,  occurred  a  culture  that  gave  only  1 
cross-over  among  130  offspring,  and  in  the  twenty-third  was  a  culture 
that  gave  Y4~g^  =  3.4  per  cent.  The  latter  value,  while  slightly  higher 
than  is  usual  for  Cm  Cn  „  is  much  lower  than  the  20  to  30  per  cent 
now  given  by  most  of  the  "high"  selected  cultures.^  The  nature  of 
this  case  has  not  yet  been  worked  out  in  detail,  though  culture  812  was 
counted  in  December  1915,  and  the  problem  has  been  worked  at 
continuously  since  that  time. 

The  following  points  now  seem  fairly  certain,  though  they  must 
still  be  checked  and  extended. 

(1)  The  "high"  value  is  due,  in  large  part,  at  least,  to  a  dominant 
gene. 

*  The  Cjji  has  apparently  been  lost,  by  crossing-over,  in  part  of  this  experiment.     But  since  the 
values  given  above  are  too  high  for  heterozygous  Cn  f,  the  discussion  given  is  not  affected. 


IN   THE    SECOND    CHROMOSOME. 


325 


(2)  This  gene  is  not  in  tlie  second  chromosome  at  all,  but  in  the 
third. 

(3)  The  third  chromosome  gene  is  Unked  to  a  gene  tluit  is  h'lluil 
when  homozygous.  This  is  the  reason  the  very  iiigh  valuen  could 
not  be  fixed. 

(4)  This  gene,  called  Cm,  ji,  also  causes  an  increase  in  p,  c  croas- 
ing-over  in  C/j^  females.  Its  effect  on  females  of  dilTorcnt  constitu- 
tions with  respect  to  Cm  and  Cur  is  not  yet  clear. 

(5)  Cjii,  JI,  when  heterozygous,  reduces  the  amount  of  cro^King- 
over  in  the  third  chromosome.  Its  effect  in  this  respect  is  similar  to, 
but  not  identical  with,  that  of  Cm  (see  next  section,  and  MuUer,  IDUi). 
Unlike  Cm,  it  "allows"  a  few  cross-overs  between  sooty  and  rough; 
but  it  causes  a  reduction  of  crossing-over  farther  to  the  left  than 
does  Ciw 

(6)  Females  with  Cnii  ii  in  one  chromosome,  and  Cm  in  its  mate, 
give  nearly  the  same  amount  of  crossing-over  in  the  third  chromo- 
some as  do  females  heterozygous  only  for  Cm,  or  perhaps  less  in  the 
left-hand  regions. 

A  detailed  comparison  of  the  effects  of  these  two  genes,  a  study  of 
their  interaction,  and  also  an  investigation  of  the  locus  of  Cm,  n  are 
now  under  way. 


COMPARISON  WITH  RESULTS  OBTAINED  FROM  Q 


/;■ 


I  have  shown  (Sturtevant,  1913a,  1915)  that  great  linkage  varLitions 
occur  in  the  third  chromosome.  My  own  unpublished  data  and  those 
presented  by  Muller  (1916)  show  that  the  case  is  very  similar  to  that 
of  diT-     The  factor  Cm,  present  in  the  beaded  stock  and  in  several 

Table  23. 


Percentage  of 

Father  of 

Culture. 

No.  of 

crossing  over. 

tested  9. 

ofTspring. 

«,«' 

^   To 

2,568a 

2,608 

291 

0.0 

0.0 

2,568a 

2,610 

284 

10.9 

14.1 

2,568a 

2,613 

197 

0.0 

»0.5 

2,568a 

2,614 

252 

0.0 

0.0 

2,568a 

2,615 

83 

7.2 

20.5 

2,568o 

2,617 

210 

0.0 

0.0 

2,568b 

2,618 

201 

0.5 

0  0 

2,5685 

2,619 

193 

0.0 

0.0 

2,5686 

2,620 

150 

11.6 

17.3 

2,568?) 

2,621 

110 

13.6 

20.9 

2,5686 

2,622 

187 

0.0 

0  0 

2,5686 

2,623 

143 

0.0 

0.0 

2,5686 

2,024 

224 

0.0 

0.0 

Total — 4  high,  9  low. 

»  Probably  an  error  in  cla.s.sification.     Surh  rr<):'.-«-ov.T.< 
are  exceedingly  rare.     This  individual  wa.s  not  tested. 


326 


INHERITED    LINKAGE    VARIATIONS 


stocks  derived  from  it  (ebony,  spread,  eosin),  greatly  decreases  cross- 
ing-over in  the  right-hand  end  of  the  third  chromosome  when  it  is 
present  in  heterozygous  form;  but  this  result  disappears  in  flies  homo- 
zygous for  Ciir-  Moreover,  the  gene  is  itself  located  in  the  region 
in  which  it  produces  its  greatest  effect.  The  following  sample  experi- 
ment will  illustrate  its  action. 

Certain  experiments  carried  out  by  Dr.  C.  B.  Bridges,  in  investi- 
gating cream  III,  led  to  the  hypothesis  that  the  eosin  stock  was  im- 
pure for  Cm-  Accordingly  two  males  from  this  eosin  stock  were 
mated  individually  to  sepia  spineless  sooty  rough  females,  and  daugh- 
ters were  back-crossed  to  sepia  spineless  sooty  rough  males,  with  the 
results  shown  in  table  23.  The  values  for  sepia  spineless  are  not  given, 
because  sepia  was  not  easily  classifiable  in  the  eosin  males  produced. 

There  are  clearly  two  quite  distinct  types  of  results  here.  In  9  of 
the  cultures  there  is  less  than  1  per  cent  crossing-over  between  spine- 
less and  rough;  in  the  other  4  there  is  about  25  to  30  per  cent  crossing- 
over  between  these  loci.^  The  results  are  due  to  the  presence  of 
Chi  in  those  females  that  gave  the  low  result,  and  its  absence  in  those 
that  gave  the  high  one.  That  the  difference  was  due  to  the  nature 
of  the  third  chromosomes  derived  from  the  fathers  was  shown  by 
testing  the  crossing-over  in  wild- type  daughters  of  these  females. 
In  every  case  such  daughters  gave  approximately  the  same  results 
as  their  respective  mothers.  Daughters  of  all  but  2615  and  2621 
were  so  tested. 

In  females  homozygous  for  Cm  the  crossing-over  between  Sg  and 
e  rises  to  about  40  per  cent  (-^|4  =  41.6  per  cent,  in  one  experiment 
selected  at  random),  as  against  about  12  per  cent  in  the  absence  of 
Cm,  and  less  than  1  per  cent  when  it  is  present  in  heterozygous  form. 
This  result  is  in  agreement  with  Muller's  (1916)  conclusion  that 
homozygous  Cm  results  in  the  production  of  more  crossing-over  than 
occurs  in  ''normal"  females. 

The  Cm  experiments  are  still  in  pro- 
gress, and  will  be  reported  in  detail  in 
connection  with  the  other  third-chromo- 
some data  accumulated  in  this  labora- 
tory. From  the  above  account,  how- 
ever, it  may  be  seen  that  the  parallel 
between  Cn  r  and  Cm  is  very  close.  The  effect  of  each  upon  the  region 
in  which  it  lies  is  shown  in  table  24.  The  s^  e  values  are  only 
approximately  correct. 

^  It  will  be  observed  that  both  males  from  eosin  stock  were  heterozygous  for  Cm  There 
was  later  found  to  be  a  lethal  near  the  Cm.  This,  in  connection  with  other  results  obtained  with 
the  eosin  stock,  suggests  that  it  was  a  "balanced  lethal"  stock  for  the  third  chromosome  (see 
Muller,  1917).  This  stock  has  now  died  out,  so  that  it  is  no  longer  possible  to  test  such  a 
hypothesis. 


Table  24. 


11-Pt  sp 

iii-s,  e 

Usual  result 

Heterozygous  C . 
Homozygous  C . . 

46.5 

2.9 

41.5 

12.0 

0.5 

40.0 

IN   THE    SECOND   CHROMOSOME.  327 

OTHER  CASES  OF  LINKAGE  VARIATIONS. 
The  cases  reported  in  this  paper  are  not  the  only  ones  in  which 
linkage  variations  are  known.  As  has  been  pointed  out  above,  there 
is  a  gene  in  the  third  chromosome  that  affects  the  percentage  of  croBs- 
ing-over  in  that  chromosome.  It  has  been  shown  (Morgan,  HU2; 
Sturtevant,  1913a;  Morgan,  Stiirtevant,  Muller,  and  Bridges,  1915; 
etc.)  that  there  is  no  crossing-over  in  the  male  of  Drosophih,  even 
between  loci  that  give  almost  50  per  cent  of  crossing-over  in  females. 
The  reverse  relation — crossing-over  in  males  but  not  in  feiruiles — 
has  been  shown  by  Tanaka  (1914)  to  hold  for  at  least  two  loci  in  the 
silkworm  moth.  Bridges  (1915)  has  show^n  that  the  percentage  may 
change  with  age,  and  Plough  (1917)  has  shown  tliat  it  may  be  chimged 
by  temperature.  Genetic  factors  (other  than  sex)  influencing  the 
process  are  suggested  by  the  results  of  Baur  (1912)  with  Ajitirrhinitni, 
of  Punnett  (1913,  1917)  with  sweet  peas,  of  Tanaka  (1913,  1914) 
with  silkworm  moths,  and  of  Chambers  (1914)  with  Drosophilu. 
In  none  of  these  cases  is  the  evidence  yet  clear  enough  to  warrant 
detailed  discussion. 

BEARING  OF  METHOD  ON  CHROMOSOME  VIEW. 

The  work  reported  in  this  paper  deals  with  the  effects  on  crossing- 
over  produced  by  certain  definite  genes.  These  genes  do  not;  so  far 
as  I  have  been  able  to  discover,  produce  any  visible  somatic  effects; 
and  their  presence  can  not  be  detected,  except  in  females,  and  in 
females  that  are  heterozygous  for  other  genes  in  definite  regions  of 
the  chromosomes,  i.  e.,  that  are  capable  of  being  tested  for  linkage 
in  those  regions.  In  the  case  of  other  females,  or  of  any  m:iles.  such 
tests  can  not  be  made  directly,  but  only  by  producing  female  de- 
scendants heterozygous  for  the  necessary  genes.  The  fact  tliat  it 
has  been  possible  to  work  out  in  great  detail  the  inheritance  of  these 
"invisible"  genes  and  the  effects  produced  by  them  is  a  striking  illus- 
tration of  the  possibilities  of  the  chromosome  view  of  inheritance  and 
of  the  advantages  of  using  a  rapidly  breeding  form  like  Drosophilu. 

The  chromosome  view  itself  is  perhaps  not  necessary  for  the  lumdling 
of  such  a  case;  but  the  conception  of  genes  that  form  independent 
groups  that  behave  as  units,  the  members  of  which  are  only  si^parable 
according  to  definite  rules,  is  necessary.  And  such  a  conception,  I 
think,  presupposes  some  material  basis  for  the  independent  groups. 
The  great  body  of  evidence  that  points  to  the  chromosomes  as  forming 
such  a  material  basis  is  too  familiar  to  need  discussion  here. 


328  INHERITED    LINKAGE    VARIATIONS 

SIGNIFICANCE  OF  MAP  DISTANCE. 

It  has  often  been  pointed  out  (e.  g.,  Sturtevant,  1913,  p.  49;  Morgan, 
Sturtevant,  Muller,  and  Bridges,  1915,  pp.  67-68)  that  1  per  cent  of 
crossing-over  must  not  be  supposed  to  represent  the  same  actual 
morphological  distance  in  different  chromosomes  or  in  different  regions 
of  the  same  chromosome.  Actual  distance  is  evidently  an  important 
factor  in  the  result.  Other  things  being  equal,  chromosome  sections 
of  equal  length  will  give  equal  percentages  of  crossing-over;  but  in  no 
case  can  we  be  certain  that  "other  things"  are  equal.  The  terms 
"distance"  and  "percentage  of  crossing-over"  have  unfortunately 
been  sometimes  used  almost  as  though  synonymous,  and  confusion 
has  perhaps  resulted.  But  it  has  been  recognized  from  the  beginning 
that  different  regions  might  show  different  frequencies  of  crossing-over 
for  the  same  actual  length  of  chromosome. 

The  results  presented  in  this  paper  show  conclusively  that  this  is 
the  case,  as  has  already  been  stated  (Morgan,  Sturtevant,  Muller, 
and  Bridges,  1915;  Muller,  1916;  Sturtevant,  1917).  They  show  that 
even  in  the  same  chromosome  pair  the  percentage  of  crossing-over 
shown  by  different  regions  is  not  only  not  always  the  same,  but  is 
not  necessarily  even  proportional.  For  example,  while  S'  b  renmins 
approximately  40.0,  h  c  may  be  either  23.0  (neither  Cni  nor  Cnr 
present),  or  7.5  (heterozygous  Cur). 

LINEAR  ARRANGEMENT  OF  GENES. 

The  strongest  evidence  for  the  linear  arrangement  of  genes  is  that 
derived  from  crosses  in  which  more  than  two  loci  in  the  same  chromo- 
some can  be  followed.  The  method  of  seriating  the  loci  on  the  basis 
of  such  information  has  been  described  in  detail  elsewhere  (Morgan, 
Sturtevant,  Muller,  and  Bridges,  1915;  Sturtevant,  1915;  Morgan  and 
Bridges,  1916),  so  need  not  be  discussed  here.  When  the  linkage 
values  are  changed  the  question  arises:  Is  the  sequence  of  genes 
affected?  It  has  already  been  shown  (Bridges,  1915;  Plough,  1917) 
that  this  sequence  is  not  altered  when  the  amount  of  crossing-over 
is  changed  by  age  or  by  temperature.  In  the  case  of  the  genetic 
changes  reported  here,  the  evidence  presented  in  tables,  1,  3,  10, 
12,  14,  17,  and  19  shows  that  the  sequence  found  in  "normal"  females 
is  maintained.  There  are  just  three  cases  in  which  the  data,  uncor- 
rected by  other  data,  might  lead  us  to  assign  a  different  sequence. 
These  three  cases  may  now  be  taken  up  in  turn. 

C        C 

(1)  In  the  case  of  r ^^ —  only  one  cross-over  between  h  and 

h  pr  Vg  ar  Sj,       -" 

Pr  was  obtained;  and  that  was  also  a  cross-over  between  p^  and  Vg. 
This  would  lead  us  to  suppose  the  sequence  to  be  Pr  b  Vg,  were  no 


IN   THE    SECOND    CHROMOSOME.  320 

Other  data  known.  But  the  other  data  for  Ci  Cur  show  con- 
clusively that  b  and  p,  give  very  little  crossinK-ovor  (0.2  per  cent) 
while  either  with  v„  c,  or  Sp,  gives  about  1.1  per  cent;  and  v  and  c 
give  only  0.1  or  0.2  per  cent  with  s,.  That  is,  v,  and  c  are 'on  the 
same  side  of  b  and  p,.  And  the  extensive  data  for  b  p,  c  show  that 
the  sequence  is  b  p,  c.  Therefore  the  one  individual  that  suggested 
the  sequence  p,  b  Vg  must  have  been  a  double  cross-over. 

(2)  In  the  case  of  CVr  only  three  cross-overs  between  c  and  «, 
were  obtained.  Of  these,  two  were  also  cross-overs  between  6  and  c, 
while  one  was  not.  These  data  alone  would  indicate  the  sequence 
as  bSpC,  instead  of  the  usual  b  c  s^.  No  great  significance  can  be 
attached  to  the  difference  between  2  flies  and  1  fly  among  a  total  of 
1,615.  In  any  case,  the  data  suggest  a  ver>'  high  coincidence.  Mcjre 
data  of  the  same  sort  will  be  necessary  before  this  exceptional  case 
can  appear  significant.^ 

C       C 

(3)  In  the  case  of  ^    ',  only  3  cross-overs  were  obsen-ed 

between  b  and  p,.  All  of  these  were  also  cross-overs  between  p,  and 
Sp.^  If  the  coincidence  in  this  case  is  100,  approximately  the  value 
usual  for  b  Pr  c,  then  nearly  half  of  the  b  p,  cross-overs  should  be  also 
Pr  Sp  cross-overs.  Therefore  the  fact  that  all  3  were  such  doubles 
need  not  cause  surprise;  even  though,  taken  alone,  it  would  indicate 
the  sequence  a^  p^  b  Sp. 

The  three  exceptional  cases  are,  then,  of  no  great  significance,  ex- 
cept as  indicating  rather  high  coincidence.  There  are  a  large  numlxr 
of  cases  in  which  the  evidence  is  much  clearer  and  in  which  the  sequence 
is  certainly  the  same  as  that  usually  found. 

HOW  DO  Cm  AND  Cur  PRODUCE  THEIR  EFFECTS? 

The  question  of  the  mechanism  whereby  the  cross-over  genes  pro- 
duce their  effects  is  not  yet  satisfactorih'  answered.  Cytological 
examination  might  conceivably  furnish  the  solution,  but  has  not  yet 
been  seriously  attempted.  A  study  of  coincidence  might  give  a  clue, 
but  is  difficult  to  make,  because  of  the  very  small  percentages  tliat  are 
concerned. 

In  the  case  of  Cur  and  Cm  it  is  to  be  noted  that  two  like  chromo- 
somes cross  over  freely,  while  two  unlike  ones  do  not.'  \Miile  this  is 
only  a  restatement  of  the  facts,  it  at  least  offers  an  attractive  o|XMiing 
for  speculation  as  to  the  nature  of  the  case. 

*In  a  culture  derived  from  Cm,  u  experiments  discussed  above,  a  female  that  wan  apparently 
of  the  constitution  r (without  Cju,  n)  has  recently  been  toatcd.     One  »,  daushter  waa 

O     Pf     C     Sp 

produced.  If  this  record  represents  what  it  appears  to,  the  count  l^ccomes  2  double  croM-OTera 
against  2  single  cross-overs. 

^Two  of  them  were  also  recorded  as  cross-overs  between  5'  and  6;  but  thia  u  prolwibly  iDcorrect. 
as  was  pointed  out  above  (p.  — ).  Cm 

'So  far  as  the  evidence  goes,  this  is  also  true  for  Cn  |,  but  t;       is  unknown. 


330 


INHERITED   LINKAGE   VARIATIONS 


Table  25. 


Loci. 

Normal. 

Cji  I  Cii  r 

Cii  I 

Cii  t 

Cm 

Cur 

Cii  I  Cii  t 
Cii  r 

Cut 
Cur 

S'b 

S'Pr 

S'c 

S'sp 

bPr 

b  Vg 

be 

b  m,- 

b  Sp 

bba 

Pr  ^0 

PrC 

37.9 

43.7 
45.9 
48.3 
62 
17.8 
22.7 
46.6 
47.6 
48.1 
11.8 
19  9 

0  0 

0.0 
0.4 
0.4 
0  2 
1.2 
1.4 
2,0 
1.6 
6.1 
1.2 
11 
2.0 
1.1 
0.2 
0.0 
0  1 

0  0 

25.9 
49.0 
0  5 
13.4 
25.4 

49.7 

42  4 

46.5 
47.3 
47.2 
6  2 
8.9 
7.4 
7.3 
9.2 

0  0 

0.1 
3.6 
3.7 
0  2 

0  3 

0.3 

38  2 

40.6 

47.5 
0  1 

49.0 
3  5 

3.1 
1.9 
3.7 

47.0 

45.0 

20  5 

47.4 
44.6 

35  3 

0.6 
16 

3.4 
2.9 
0.0 
0.0 
0  1 

2  9 

1.9 
3.6 

Pr  Sp 

^oSp 

c  rrif 

46.5 
35.9 

47.4 

41  5 

0.0 
0  1 

C  Sp 

Total». . 

30  2 

94.2 

1.4 

56.3 

50.3 

3.2 

47.8 

83.2 

'^  S'  b  -\-  b  Pr  -\-  Pr  c  '\'  c  Sp,  except  in  the  last  two  columns,  where  pr  Sp  is  used.  Probably 
all  but  the  second  and  fifth  columns  are  too  low,  since  no  correction  has  been  made  for  unob- 
servable  double  cross-overs. 

SUMMARY. 

Two  genes  that  affect  the  amount  of  crossing-over  in  the  second 
chromosome  are  discussed.  Females  of  various  constitutions  with 
respect  to  these  genes  give  the  results  shown  in  table  25  and  figure  1. 
Cm,  located  somewhere  to  the  left  of  purple,  decreases  the  amount 
of  crossing-over  between  star  and  purple  in  females  heterozygous  for 
it.  Cjir,  located  between  purple  and  speck,  reduces  the  amount  of 
crossing-over  between  purple  and  speck  in  females  heterozygous  for 
it;  but  females  homozygous  for  Cur  show  the  usual  amount  of 
crossing-over. 

Neither  of  these  genes  causes  any  change  in  the  usual  condition  of 
no  crossing-over  in  males. 

An  incompletely  investigated  case  of  increased  crossing-over  be- 
tween purple  and  curved  is  apparently  due,  in  part  at  least,  to  a 
dominant  third-chromosome  gene. 

A  cross-over  gene,  located  in  the  third  chromosome,  affects  that 
chromosome  in  much  the  same  way  that  Cur  affects  the  region  in 
which  it  lies. 

In  all  these  cases  the  amount  of  crossing-over  is  changed,  often 
markedly  so.  But  the  sequence  of  the  genes  is  unchanged ;  and  females 
of  any  one  constitution  give  as  consistent  results  as  do  ''normal" 
females. 


APPENDIX. 


DETAILED  DATA. 


In  the  following  tables  it  is  to  be  understood  that  when  a  theoretically 
possible  cross-over  class  is  not  set  down  no  flies  represcntinR  such  a  crosb- 
over  appeared  in  the  series  involved. 


Table  26. 
One  original  Nova  Scotia  chromosome. 


Culture. 

Non-cross-overa. 

Cro«»-oveni. 

Toul. 

+ 

b  nif 

b 

ntr 

645 

98 
96 

38 
40 

0 
2 

1 
2 

137 
140 

646 

Total 

194 

78 

2 

3 

277 

Culture. 

Non-cross-overe. 

Cross-overe. 

Toul. 

+ 

VffSp 

^t 

»P 

7 

55 
75 

72 
61 

32 
156 
IGl 

44 
59 
46 
52 
23 
169 
178 

0 
2 

2 
0 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 

99 
1.16 
120 
113 

55 
325 
339 

68 

69 

109 

170 

199 

200 

Total 

612 

571 

4 

0 

1,187 

Culture. 

Non-crose-overs. 

Crosa-ovcfB. 

Toul. 

+ 

C  Sp 

c 

•p 

111 

89 
143 
66 
87 
79 
99 

86 
61 
122 
56 
63 
23 
86 

0 
0 
0 
0 
0 
0 
0 

1 

0 
0 
0 
0 
0 
0 

198 
15() 

122 
IM 
102 
185 

281 

308 

310 

527 

541 

Total 

674 
109 

497 
99 

0 
0 

1 

0 

1,172 
20S 

527ai 

*  Second  brood  of  same. 


3.31 


332 


APPENDIX. 


Table  26 — continued. 


Culture. 

Non-cross-over.s. 

Cross-overs. 

Total. 

+ 

b  PfCnir 

1 

2 

1, 

2 

b 

Pr  C  nir 

b  Pr 

c  mj. 

Pr 

b  c  vit 

675 

67 

49 

0 

1 

3 

2 

0 

0 

122 

683 

132 

125 

0 

0 

1 

0 

0 

0 

258 

691 

84 

38 

0 

0 

1 

4 

0 

0 

127 

691a.... 

101 

66 

0 

0 

1 

2 

0 

0 

170 

692 

123 

106 

0 

0 

0 

1 

0 

0 

230 

695 

105 

79 

0 

0 

0 

0 

0 

0 

184 

726 

104 

83 

0 

0  • 

4 

7 

1 

0 

199 

727 

105 

43 

0 

0 

1 

1 

0 

0 

150 

758 

54 

62 

0 

0 

0 

3 

0 

0 

119 

759 

97 

89 

0 

0 

2 

1 

0 

0 

189 

760 

61 

45 

0 

0 

2 

3 

0 

0 

111 

761 

96 

69 

0 

0 

1 

2 

0 

0 

168 

762 

Total .  . 
675ai . .  . 

73 

52 

0 

0 

0 

0 

0 

0 

125 

1,202 

906 

0 

1 

16 

26 

1 

0 

2,152 

163 

112 

0 

3 

0 

2 

0 

0 

280 

684ai . . . 

145 

112 

0 

0 

0 

2 

1 

0 

260 

69161. 

164 

124 

0 

0 

2 

2 

0 

0 

292 

692o* .  .  . 
Total .  . 

52 

62 

0 

0 

1 

0 

1 

0 

116 

524 

410 

0 

3 

3 

6 

2 

0 

948 

1  Second  broods  from  675,  684,  691,  and  692  above. 


Non-cross-overs. 

Cross-overs. 

Total. 

Culture. 

S'bp^ 

+ 

2 

S'b 

Px 

733            

91 

88 

103 
102 

3 
3 

3 
3 

200 
196 

735 

Total 

179 

205 

6 

6 

396 

Culture. 

Non-cross-overs. 

Cross-overs. 

Total. 

+ 

b   Pr  c 

1 

2 

1.2 

b 

PtC 

b  Pr 

c 

Pt 

b  c 

368 

369 

370 

410 

411 

412 

434 

436 

437 

441 

442 

443 

444 

445 

90 

124 

82 

67 

100 

94 

236 

88 

82 

151 

112 

156 

124 

247 

42 

70 

57 

33 

68 

80 

160 

87 

43 

126 

76 

125 

101 

227 

0 
0 
0 
0 
1 
0 
0 
0 
1 
0 

1 
1 

0 

1 

0 

1 

0 
0 

1 

0 

1 

0 
0 
0 

0 
0 
0 

1 

0 
0 
3 
0 
3 
1 
1 
0 
0 
2 

1 
1 
0 
0 

0 
1 
0 
0 
2 

0 
0 
0 
0 
2 
2 
2 

0 
0 

0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 

1.32 
196 
142 
100 
175 
175 
398 
175 
126 
281 
192 
285 
225 
476 

APPENDIX. 


333 


Table  26 — continued. 


Culture. 


460 ... . 
461.. . . 
462.... 
463 ... . 
464 ... . 

474 

475 

476 

477.... 

494.... 

501 ... . 

•  502 ... . 

503 

505.... 
507.... 
553.... 
664.... 
681.... 
601 ... . 
639.... 
676.... 
677.... 
678.... 

679 

680 

681 

681o... 

682 

684 

685 

693 

694 

Total .  . 

478> 

502a' .  . . 

510' 

6OI0I.  .. 
694a> .  . . 

Total .  . 


Non-cros.s-overs. 


+ 


211 

201 

200 

165 

133 

166 

58 

140 

107 

82 

94 

112 

122 

84 

64 

87 

113 

74 

115 

97 

106 

116 

134 

122 

123 

132 

92 

104 

137 

116 

91 

98 


5,549 


109 

113 

142 

87 

94 


545 


Pr  c 


170 

132 

136 

103 

81 

95 

41 

136 

58 

66 

100 

77 

122 

56 

34 

70 

77 

54 

74 

87 

72 

43 

66 

73 

76 

107 

73 

54 

64 

53 

65 

63 


Cro8»-over8. 


3,873 


82 
75 
81 
52 
93 


3 

3 

1 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

1 

0 

0 

0 

0 

0 

1 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 


PtC 


14 


383 


0 
0 
0 
0 
0 


1 
0 
0 

0 

1 

0 
0 
0 
0 
0 
0 
0 

n 
0 
0 
0 
0 
0 
0 
1 
3 
0 
0 
1 
0 
1 
0 
0 
0 
0 
0 
0 


hp, 


12 


0 
0 
0 
0 


0 

1 
1 
1 
1 
2 
0 
0 
3 
1 
2 
2 
1 
1 
2 
0 
0 
2 
1 
2 

1 
2 

1 
1 
0 
0 
1 
1 
0 
2 

0 
0 


44 


4 
0 
1 
1 
0 


0 
2 
0 
0 
1 
1 
0 
1 
5 
■) 

(I 
1 

0 
1 
0 
0 
1 
1 
0 
I 
2 
0 
3 
1 
0 
3 
0 
1 
2 

0 
0 
0 


38 


5 
0 
3 
0 
1 


'  Second  broods  from  above. 


1.2 


Pr 


0 
0 
1 

0 
U 
1 

0 

1 

0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 


0 
0 

1 

0 
0 


6c 


0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 


0 
0 
0 
0 
0 


Toul. 


9,633 


386 
330 
330 
2M 

217 
•2fA 
W 
27H 
173 
161 
106 
102 
246 
143 
100 
167 
101 
131 
lOf) 
1K9 
IM 
161 
204 
108 
100 
243 
166 
160 
2a3 
171 
166 
161 


202 
188 
228 
140 
188 


046 


Culture. 

Non-cross-ovcrs. 

Single  cro8»K)vcrB. 

Toua. 

+ 

b  Pr  vg  iflr)  Sp 

0 

3 

4 

bpr 

Vg  (Or)  Sp 

b  Pr  T,  (a,) 

'p 

258 

259 

262 

304 

656 

669 

Total .... 

121 
127 

77 
129 
146 

64 

61 
74 
41 
93 
99 
51 

1 
1 
0 
2 
2 
0 

0 

1 
0 

1 
1 
1 

0 
0 
0 

(1 

0 
0 

0 
0 
0 

(1 
0 
0 

0 
0 

1 

0 
0 
0 

183 
203 
119 
226 
24H 
116 

664 

419 

6 

4 

0 

0 

1 

1,004 

334 


APPENDIX. 


Table  26 — continued. 


Non-cross-overs. 

Cross-overs. 

Total. 

+ 

S'  b  pj-  c  Sp 

2 

3 

S'b 

PrCSp 

S'bpr 

C  8p 

819 

819a' 

112 
108 

110 
111 

0 
1 

0 
0 

1 
0 

0 
2 

223 
222 

1  Second  brood  from  above. 


Speck  End  Replaced. 

Culture. 

Non 

-cross-overs. 

Cross-overs. 

Total. 

-1- 

b  Pr  Vj  (ar)   Sp 

2 

1.2 

b  Pr 

Vg  (Or)  Sp 

Pt 

b  Vg   (ar)    Sp 

422 

133 

144 

3 

2 

1 

0 

283 

Culture. 

Non-cross- 
overs. 

Cross-overs. 

Total. 

Culture. 

Non-cross- 
overs. 

Cross- 
overs. 

Total. 

1 

2 

+ 

b  PrC 

b 

Sp 

+ 

bsp 

b 

PrC 

bpr 

c 

477 

492 

Total. 

175 
116 

97 
90 

1 
0 

0 
0 

4 
1 

1 
0 

278 
207 

337 

341 

Total. 

125 
118 

188 
134 

2 
3 

0 
2 

315 
257 

291 

187 

1 

0 

5 

1 

485 

243 

322 

5 

2 

572 

One  Reconstituted  Nova  Scotia  Chromosome. 


Culture. 

Non-cross-overs. 

Cross-overs. 

Total. 

+ 

b  Pr  c  Sp 

2 

b  Pr 

C  Sp 

786 

787 

Total  . 

138 
1.37 

141 
133 

4 

1 

0 

1 

283 

272 

275 

274 

5 

1 

555 

Heterozygous  Cuf. 


Culture. 

Non-cross- 
overs. 

Cross- 
overs. 

Total. 

Culture. 

Non-cross- 
overs. 

Cross- 
overs. 

Total. 

+ 

b  Pr 

b 

Pr 

+ 

be 

b 

c 

352 

353 

Total . . 

142 
151 

143 

142 

8 
4 

3 
10 

296 
307 

468 

72 

65 

10 

7 

154 

293 

285 

12 

13 

603 

APPENDIX. 


335 


Table  26 — continued. 


Culture. 

Non-cros3- 
overa. 

Croaa- 
overa. 

Total. 

Culture. 

Non-crosa- 
overs. 

Cr«M- 
overa. 

Total. 

b 

c 

+ 

be 

+ 

b  tht 

b 

m. 

277 

377 

379 

380 

Total .  . 

64 
104 
114 

55 

38 

133 

80 

65 

3 

9 

10 

3 

0 
9 
9 
5 

105 
255 
213 
128 

653 

654 

655 

Total  . 

183 

146 

80 

97 
89 
95 

12 
11 
10 

I 
2 

8 

203 
248 
103 

409 

281 

33 

11 

734 

337 

316 

25 

23 

701 

Culture. 

Non-cross- 
overs. 

Croas- 
overa. 

Total. 

Culture. 

Non-orosa- 
overs. 

Croiw- 
overs. 

Total. 

+ 

pcr 

Pr 

c 

+ 

C  Sp 

c 

•» 

351 

495 

517 

Total .  . 

64 

173 

70 

69 
1.56 

77 

4 
0 
0 

2 
0 
0 

1.39 
329 
147 

226 

102 

44 

0 

0 

146 

307 

302 

4 

2 

615 

Heterozygous  Cuf. 


Non- 

Croaaovera. 

Culture. 

croaaovers. 

Total. 

+ 

1 

2 

1. 

2 

b  Pr  c 

b 

PrC 

b  Pr 

c 

Pr 

6c 

318 

136 

91 

7 

6 

2 

1 

0 

0 

243 

354 

106 

105 

7 

4 

4 

0 

0 

0 

226 

355 

103 

81 

7 

4 

1 

1 

0 

0 

197 

416 

72 

42 

3 

6 

0 

0 

0 

1 

124 

417 

109 

49 

8 

4 

3 

2 

0 

0 

175 

430 

96 

77 

9 

4 

1 

4 

0 

0 

191 

431 

1.36 

114 

4 

10 

6 

0 

0 

0 

270 

432 

143 

111 

7 

8 

3 

2 

0 

0 

274 

433 

80 

53 

2 

3 

0 

0 

0 

0 

138 

446 

177 

179 

9 

6 

0 

1 

1 

0 

373 

448 

58 

39 

1 

1 

1 

0 

0 

0 

100 

449 

142 

124 

2 

2 

0 

0 

1 

0 

271 

450 

156 

151 

6 

8 

1 

1 

0 

0 

323 

467 

196 

167 

14 

11 

5 

1 

0 

1 

395 

469 

205 

191 

11 

15 

4 

2 

1 

1 

4.10 

470 

184 

124 

21 

18 

3 

3 

0 

0 

353 

471 

178 

136 

10 

16 

2 

4 

0 

0 

346 

472 

178 

147 

7 

10 

3 

0 

0 

0 

345 

473 

145 

95 

2 

5 

6 

1 

0 

0 

254 

480 

177 

104 

7 

2 

4 

3 

0 

0 

297 

496 

132 

89 

7 

4 

1 

3 

1 

0 

237 

500 

137 

122 

7 

8 

1 

1 

1 

0 

277 

511 

Total .  . 
450a» .... 

51 

49 

2 

4 

2 

1 

0 

0 

109 

3,096 

2,440 

160 

1.59 

53 

31 

5 

3 

5,947 

95 

100 

7 

7 

4 

4 

1 

0 

218 

472ai 

Total .  . 

114 

102 

23 

14 

6 

3 

1 

0 

263 

209 

202 

30 

21 

10 

7 

2 

0 

481 

1  Second  brooda  from  450  and  472  above. 


336 


APPENDIX. 


Table  26 — continued. 


Culture. 

Non- 
crossovers. 

Crossovers. 

Total. 

bpr 

c 

1 

2 

1.2 

Pr 

6c 

+ 

b  PrC 

6 

PrC 

686 

687 

707 

708 

709 

719 

721 

Total . 

707ai... 
TOSaK.. 

Total. 

114 
52 
48 
44 
53 
94 

108 

89 
49 
55 
62 
44 
67 
94 

6 

5 

3 

11 

1 
1 

8 

4 
3 
6 
2 

1 
7 
7 

4 
1 
0 
0 
1 
0 
0 

3 
2 
0 
2 
0 
0 
3 

0 
0 
1 
0 
0 
0 
0 

1 
0 
0 
0 
0 
0 
0 

221 
112 
113 
121 
100 
169 
220 

513 

460 

35 

30 

6 

10 

1 

1 

1,056 

107 
108 

82 
122 

10 
6 

1 
2 

1 
0 

1 
1 

0 
0 

0 

1 

202 
240 

215 

204 

16 

3 

1 

2 

0 

1 

442 

Culture. 

Non- 
crossovers. 

Crossovers. 

Total. 

b 

PrC 

1 

2 

+ 

b  PrC 

Pr 

be 

512    

136 
142 

104 
118 

11 
23 

6 
3 

0 
1 

2 
0 

259 

287 

513 

Total 

278 

222 

34 

9 

1 

2 

546 

Culture. 

Non- 
crossovers. 

Crossovers. 

Total. 

+ 

bpfSp 

1 

2 

b 

PrSp 

bpr 

Sp 

569 

101 

74 

92 
80 

7 
2 

0 
5 

3 
1 

3 

1 

206 
163 

702 

Total 

175 

172 

9 

5 

4 

4 

369 

Culture. 

Non- 
crossovers. 

Crossovers. 

Total. 

bpr 

Sj, 

1 

2 

1.2 

b  Sp 

Pr 

+ 

bprSp 

b 

PrSp 

545 

546 

547 

Total . 

546a2..  . 

97 
99 
73 

91 
91 
90 

6 

15 

4 

22 

22 

3 

11 

13 

3 

12 

14 

0 

0 
1 
5 

2 
3 
0 

241 

258 

178 

269 

272 

25 

47 

27 

26 

6 

5 

677 

106 

128 

26 

24 

17 

18 

3 

1 

323 

•  Second  broods  of  707  and  708  above. 
'  Second  broods  of  546  above. 


APPENDIX. 
Table  26 — continued. 


337 


Culture. 

Non- 
crossovers. 

Crossovers. 

Non- 
croHuovcrn. 

ovcm. 

ToUU. 

+ 

b   Tg  Sp 

1 

Total. 

Culture. 

62 

1 

b 

Vg    sp 

b     Pf    «jr 

1 

Pr»p 

fcr, 
7 

648 

648ai 

85 
122 

56 
95 

11 
3 

4 
2 

156 
222 

622 

39 

9 

117 

Culture. 

Non- 
crossovers. 

Crossovers. 

Tot*l. 

-S' 

b  PrSp 

1 

2 

3 

1,  2 

1.  3 

2.  3 

4 

b 

S's 

p  bpr 

S'b 

PrSp 

60 

Sp 

S'P 

r   bip 

696 

699 

715 

716 

717 

Total . 

696a2 . . . 
699a2 . . . 

Total. 

45 
20 
61 
37 
39 

47 
27 
60 
42 
42 

26 
20 
38 
20 
29 

48 
15 
45 
24 
32 

5 

2 
1 
3 
3 

2 
1 
6 
2 
1 

4 
1 
0 
0 
2 

0 
0 
2 
0 

1 

1 
0 

2 
0 
0 

2 

1 
2 
0 
1 

0 

1 

0 
0 
0 

1 
1 
0 
0 
0 

0 
0 
0 
0 

1 

0 
1 
0 

0 
0 

181 
90 
217 
128 
151 

202 

218 

133 

164 

14 

12 

7 

3 

3 

6 

1 

2 

1 

1 

767 

63 
17 

55 

28 

50 
23 

46 
20 

1 
2 

2 
6 

1 
0 

0 
1 

0 
0 

2 
1 

0 

1 

0 

1 

0 
0 

0 
0 

220 
100 

80 

83 

73 

66 

3 

8 

1 

1 

0 

3 

1 

1 

0 

0 

320 

Culture. 

Non-erossovers. 

Crossovers. 

Total. 

+      b 

Pr  c  rrir 

1 

2 

b 

Pr  c  rrir 

b  Pr 

C  TO, 

723          

93 
115 
101 

64 

82 
94 
79 
72 

1 

7 
4 
9 

3 

7 
5 
3 

2 
4 
5 
3 

4 

5 
1 
2 

185 
232 
195 
153 

724 

725 

763 

Total 

373 

327 

21 

18 

14 

12 

765 

Culture. 

Non-en 

jssovers. 

Crossovers. 

Total. 

Sp 

b  pr  c 

1 

2 

1.  2 

bsp 

PrC 

b  Pr  8p 

c 

Pr«p 

be 

742    

142 

136 

71 

112 

150 

143 

56 

1.33 

8 

4 

8 

10 

8 
6 
6 
9 

1 

1 
0 
3 

2 

1 
1 
3 

0 
0 
0 

1 

0 
0 
0 
0 

311 
291 
142 
271 

743 

747 

749 

Total 

461 

482 

30 

29 

5 

7 

1 

0 

1,015 



i 

1 

^  Second  brood  of  above. 


^  Second  broods  of  696  and  699,  above. 


338 


APPENDIX. 


Table  26 — continued. 


Non- 

Crossovers. 

Culture. 

crossovers. 

1 

2 

3 

4 

S'bsp 

PrC 

S'PrC 

b  Sp 

S'bpr'' 

Sp 

S'bc 

PrSp 

S'b 

PrCSp 

796            

82 
68 
82 
71 
73 
56 

69 
52 
56 
54 
70 
72 

71 
42 
49 
36 
60 
53 

73 
42 
54 
59 
66 
52 

5 

4 
13 

7 
6 
6 

11 
5 

8 
7 
9 
5 

1 
0 
3 
1 
2 
0 

0 
2 

1 
3 
1 
3 

0 
0 
0 
0 
0 
0 

0 
0 

1 

0 

«  i 

797       

798     

799          

800          

801              

Total 

432 

373 

311 

346 

41 

45 

7 

10 

0 

1  ! 

796a'    

90 

68 
80 

68 
65 
64 

62 
45 
30 

64 
53 

38 

4 
7 
0 

6 

8 

7 

6 
3 

1 

2 
2 
2 

0 
0 
0 

0 
0 
0 

797a'            

798a'              

Total 

238 

197 

137 

155 

11 

21 

10 

6 

0 

0 

Culture. 

Cross 

Continued.                                                                 j 

1.2 

1,  3 

2,  3 

2,  4 

3.4 

1.  2,  3 

1 

Total.  1 

S'sp 

b  PrC 

S'  Pr  Sp 

be 

S'  b  Pr  Sp 

c 

S'bprC  Sp 

+ 

S'  be  Sp 

Vt 

S'c 

b  Pr  Sp 

796 

797 

798 

799 

800 

801 

Total. . 

796a' .... 

797a' 

798a' .... 

Total. . 

5 
3 
0 
1 
3 
0 

5 
2 
2 

6 

4 

1 

1 
1 
0 
0 
0 

1 

0 
0 
0 
1 
2 
5 

1 
0 
0 
0 
0 
0 

1 

0 
0 
0 
0 
0 

0 
0 
0 
0 
0 

1 

0 
0 
0 

0 
0 
0 

0 
0 
0 
0 
0 
0 

1 
0 
0 
0 
0 

1 

0 
0 
0 
2 
0 
0 

0 
0 
0 
0 
0 
0 

325 

221 
269 
248 
296 
256 

12 

20 

3 

8 

1 

1 

1 

0 

0 

1 

2 

0 

1,615 

1 
1 
4 

0 

1 
2 

0 
4 
0 

1 
0 
0 

2 
0 

0 

1 

0 

0 
0 
0 

0 

0 
0 

0 
0 
0 

0 
0 
0 

0 

1 
0 

1 
0 
0 

307 
259 

228 

6 

3 

4 

1 

2 

1 

0 

0 

0 

0 

1 

1 

794 

'  Second  broods  from  796,  797,  and  798  above. 


Culture. 

Non- 
crossovers. 

Crossovers. 

Total. 

S'h 

c 

2 

S'hc 

+ 

776 

795 

Total. 

795a'.... 

52 
51 

54 
43 

22 
8 

16 

8 

144 
110 

103 

97 

30 

24 

254 

51 

45 

6 

5 

107 

I 


^  Second  brood  of  795,  above. 


APPENDIX.    . 

Table  26 — continued. 


339 


Non- 

Non- 

cross- 

Crossovers. 

eroHH- 

CroHnovem. 

Culture. 

over3. 

Total. 

Culture. 

overa. 

ToUl. 

1.. 

1 

2 

1 

2 

1.2 

(^ 
« 

+ 

_e. 

05 

+ 

i: 

6 

_5« 

hpr 

c^ 
t 

i- 

b 

•• 

bpr 

'P 

Pr 

6,, 

pO 

P. 

-o 

i: 

1 

404 

114 

84 

7 

3 

2 

0 

210 

785 

64 

74 

0 

1 

54 

65 

0 

240 

Culture. 

Non- 
crossovers. 

Cro8.sovers. 

Total. 

b  Pr  Sp 

c 

2 

3 

2.  3 

b  prc 

Sp 

bpr 

C  Sp 

+ 

bprCBp 

794 

794a  1... 

41 
76 

50 
61 

17 
19 

18 
17 

46 
47 

22 
35 

1 
6 

5 
0 

200 
261 

^  Second  brood  of  794,  above. 
Cii  f 


Culture. 

Non- 
crossovera. 

Crossovers. 

Total. 

S'  b  Pr  Sp 

c 

2 

3 

4 

5' 6c 

PrSp 

S'bpr 

C  Sp 

S'bpr 

C  «p 

789 

790 

791 

Total . 

789a  1... 
791a  1.. . 

Total . 

112 

95 

107 

116 
124 
105 

0 
0 
1 

0 
0 
0 

5 

1 
6 

5 
1 
6 

0 

1 
0 

0 
0 
0 

238 
222 
225 

314 

345 

1 

0 

12 

12 

1 

0 

685 

141 
115 

117 
124 

0 
0 

0 
0 

3 

1 

4 
3 

0 
0 

1 

0 

266 
243 

256 

241 

0 

0 

4 

7 

0 

1 

509 

1  Second  broods  of  789  and  791  above. 


Culture. 

Non- 
crossovers. 

Crossovers. 

Total. 

Culture. 

Non- 
crossovers. 

Crossovers, 

Total. 

b  Pr 

c  nif 

2 

b  Pr 

c 

1 

2 

-f 

b  Pr  CTTir 

Pr 

6c 

+ 

6  Pr  c 

713 

752 

753 

Total. . 

95 

126 

94 

103 
131 

82 

6 

1 
0 

3 
1 
1 

207 
259 

177 

754 

778 

Total . 

48 
61 

58 
59 

1 
0 

1 
0 

2 
6 

0 
2 

110 
128 

109 

117 

1 

1 

8 

2 

238 

315 

316 

7 

5 

643 

340 


APPENDIX. 


Table  26 — continued. 


Non- 
crossovers. 

Crossovers. 

Total. 

Culture. 

1 

3 

1,3 

1.  2,  3 

S'  h  Pr Sp 

+ 

S' 

b  Pr  Sp 

S'bpr 

Sp 

S'sp 

bPr 

S'Pr 

b  Sp 

736 

54 
78 
37 

47 
71 
35 

1 
0 
0 

{ 

3 
D 
2 

39 
61 
41 

44 
66 
36 

0 
0 
0 

0 
0 
0 

1 

1 
0 

0 
0 
0 

186 
277 
151 

738 

739 

740 

39 

50 

0 

( 

') 

32 

27 

0 

0 

0 

0 

148 

779 

73 

73 

0 

0 

68 

72 

0 

0 

0 

0 

286 

780 

31 

49 

0 

0 

29 

30 

0 

0 

0 

0 

139 

782 

45 

73 

0 

0 

40 

52 

0 

0 

0 

0 

210 

783 

59 

60 

0 

0 

56 

64 

1 

0 

0 

0 

240 

784 

Total 

84 

89 

0 

0 

91 

94 

0 

0 

0 

0 

358 

500 

547 

1 

2 

457 

485 

1 

0 

2 

0 

1,995 

Culture. 

Non- 
crossovers. 

Cros 

sovers 

• 

Total. 

Culture. 

Non- 
crossovers. 

Cross- 
overs. 

Total. 

o 

1, 

2 

+ 

bprSp 

b 

Sp 

+ 

b  Sp 

bpr 

Sp 

Pr 

bsp 

660 

27 

31 

18 

24 

0 

1 

101 

340 

72 

72 

70 

49 

263 

670 

Total . 

55 

41 

49 

47 

0 

0 

192 

82 

72 

67 

71 

0 

1 

293 

(^11  T 


Culture. 

Non- 
crossovers. 

Crossovers. 

To< 

S'b 

PrSp 

1 

2 

3 

1,  2 

1,  3 

2.3 

1,  2,  3 

S'prSp 

b 

S'bprSp 

+ 

S'bsp 

Pr 

S' 

bpj-sp 

S'Pr 

b  Sp 

S'bpr 

Sp 

S'sp 

bpr 

885.... 
886.... 
887.... 
888.... 

Total. 

40 
44 
17 
54 

43 
47 
27 
31 

26 
30 
14 
24 

30 
31 
14 
23 

3 

1 
1 
3 

2 
0 
0 
6 

30 
37 
15 

45 

27 
39 
29 
20 

0 
0 
0 
0 

0 

1 
1 
0 

23 

22 

7 

32 

16 
18 
17 
21 

1 
4 
1 
2 

2 
1 
0 
1 

0 

1 
0 
0 

0 

2 

1 
0 

24< 
27i 
14- 
2Qi 

155 

148 

94 

98 

8 

8 

127 

115 

0 

2 

84 

72 

8 

4 

1 

3 

92; 

Culture. 

Non- 
crossovers. 

Crossovers. 

Total. 

Culture. 

Non- 
crossovers. 

Crossovers. 

b  Pr 

Sp 

1 

2 

1,  2 

b 

Sp 

+ 

b  Sp 

Tot 

b  Sp 

Pt 

+ 

bprSp 

b 

PrSp 

745 

75 
79 

90 
51 

2 
4 

1 
2 

41 
43 

30 

47 

1 
0 

3 
2 

243 

228 

623 

41 

36 

39 

35 

16 

748.... 

Total 

154 

141 

6 

3 

84 

77 

1 

5 

471 

LITERATURE  CITED. 


Baur,  E.     1912.     Vererbungs-und   BastaniicrunKSvorsuohc  niit    ATUirrhinum.     II.  Fak- 

torenkoppclung.     Zts.  ind.  Abst.  V'crorb.  6:  201. 
Bkidges,  C.  B.     1915.     A  linkage  variation  in  Draso/>//i/a.     Journ.  KxpiT.  Zool.,  19;  I. 
,  and  T.  H.  Morg.\n.     1919.     The  second  chromosome  group  of  mutant  characters. 

This  publication. 
Chambers,  R.     1914.     Linkage  of  the  factor  for  bifid  wing.     Biol.  Bull.  27;  151. 
Morgan,  T.  H.     1912.     Complete  linkage  in  the  second  chromosome  of  the  male.     Science, 

n.s.,  36:719. 
.     and  C.  B.  Bridges.    1916.    Sex-linked  inheritance  in  Drosophila.    Carnegie  Inat. 

Wash.  Pub.  237. 
,  A.  H.  Sturtevant,  H.  J.  Muller,  ami  C.  B.  Bridges.     191.j.     'Ihe  mechanism 

of  Mendelian  heredity.     New  York. 
Muller,   H.  J.     1916.     The  mechanism  of  cros.sing-over.     Amer.   Nat.  50;   193,   284, 

350,  421. 

.  1917.     An  Oenothera-like  case  in  Drosophila.     Proc.  Nat.  Acad.  Science,  3;  619. 

Plough,  H.  H.     1917.     The  effect  of  temperature  on  crossing-over  in  Drosophila.     Journ. 

Exper.  Zool.  24;  147. 
Punnett,  R.  C.     1913.     Reduplication  series  in  sweet  peas.     Journ.  Genet.,  3;  77. 

.     1917.     Reduplication  series  in  sweet  peas.     II.     Journ.  Gonot.,  6;  185. 

Sturtevant,  A.  H.     1913.     The  linear  arrangement  of  six  .sex-linked  factors  in  Droao- 

phila,  as  shown  by  their  mode  of  association.     Journ.  Exper.  Zool.,  14;  43. 
.     1913a.     A  third  group  of  linked  genes  in   Drosophila  ampelophila.    Science, 

n.s.,  37,  990. 
.     1915.     The   behavior   of   the   chromosomes  as  studied  through  linkage.     Zts. 

ind.  Abst.  Vererb.,  13;  234. 
.     1917.     Genetic  factors  affecting  the  strength  of  linkage  in  Drosophila.     Proc. 

Nat.  Acad.  Science,  3;  555. 
Tanaka,  Y.     1913.     Gametic  coupling  and  repulsion  in  silkworms.     Journ.  Coll.  Agr. 

Tohoku  Imperial  Univ.,  Sapporo,  Japan,  5;  115. 
.     1914.     Further  data  on  the  reduplication  in  silkworms.     Journ.   Coll.   Agr., 

Tohoku  Imper.  Univ.,  Sapporo,  Japan,  6;  1. 

341 


IV. 


A  DEMONSTRATION 
OF  GENES  MODIFYING  THE  CHARACTER  "NOTCH." 


By  T.  H.  Morgan. 


343 


A  DEMONSTRATION  OF  GENES    MODIFVIXCr    TIIK 

CHARACTER  "NOTCH." 


By  T.  H.  Morgan. 


Two  main  topics  are  dealt  with  in  the  following  pa^cs  fnjin  the 
standpoint  of  the  experimental  results  obtained.  One  of  them  con- 
cerns the  demonstration  of  modifying  genes  that  were  involved  in  the 
results  of  a  selection  experiment.  The  other  topic  is  a  discussion  of 
the  possibility  of  contamination  of  genes  as  a  method  that  luus  l>een 
appealed  to  as  an  influence  vitiating  the  regularity  of  Mendelian 
phenomena. 

The  claim  of  the  Mendelians  that  genes  have  been  found  to  l>e  sta- 
ble in  successive  generations  wherever  a  critical  test  of  them  was  made 
has  been  challenged  both  on  the  grounds  of  empiric  observation  and 
on  the  more  sentimental  grounds  that  such  hard  and  fa^t  rules  do  not 
apply  to  living  things  which  are  rather  to  be  thought  of  as  variable 
quantities.  In  the  following  pages  an  account  is  given  of  a  character 
that  changed  in  the  course  of  selection  and  a  demonstration  that  the 
result  was  due  to  a  modifying  gene  and  not  to  contamination  between 
the  notch  gene  and  its  normal  allelomorph,  despite  the  fact  tliat  an 
exceptional  opportunity  was  given  to  contaminate  the  gene,  if  contami- 
nation is  a  possible  process. 

In  1915,  Dexter  described  a  mutant  type  of  Drosophih  called  Notch 
or  "perfect  Notch,"  and  made  out  the  main  points  in  the  heredity  of 
the  character.  The  gene  is  sex-linked,  and  dominant  for  the  serra- 
tion that  it  produces  in  the  wings,  but  recessive  in  its  lethal  effect. 
Since  the  gene  is  carried  by  the  X  chromosome,  any  male  that  gets  a 
chromosome  with  this  gene  dies,  while  the  female  that  has  another  X 
carrying  the  normal  allelomorph  lives  and  shows  the  notch  at  the  end 
of  her  wings  (fig.  91).  Since  no  male  that  has  the  notch  gene  can  live, 
it  is  not  feasible  to  determine  whether  a  female  containing  two  letluil 
bearing  X's  would  also  die.^  Every  heterozygous  Notch  fcnuile  gives 
twice  as  many  daughters  as  sons,  because,  as  stated,  half  of  the  sons 
die,  namely,  those  that  get  the  lethal-bearing  X".  The  scheme  is  iis 
follows : 

X-X"  eggs 

X  —  Y   sperm 

XX  —  Xr*  —  XY  —  X^Y  (dies) 
9  9  cf  d" 


1  Unless  an  XX  egg,  arising  through    "equational  non-di.sjunrtion,"  were  fcrtilued  by  a  Y 
sperm  and  lived.     No  such  females  have  appeared.     They  would  have  no  rcRuinr  i»on9. 

345 


346 


GENES   MODIFYING   NOTCH. 


Half  of  the  daughters  are  normal,  half  are  heterozygous  Notch. 
The  normal  daughters  and  normal  sons  never  transmit  the  Notch 
gene,  which,  therefore,  never  gets  into  the  male  hne  or  into  the  line  of 
normal  daughters. 


Fig.  91. 


Dexter  obtained  his  mutant  in  a  cross  between  beaded  and  wild. 
The  Notch  that  I  used  arose  independently  in  descendants  of  ves- 
tigial flies,  in  which  stock  the  factor  may  have  already  existed.  This 
mutant  has,  however,  originated  several  times  in  other  cultures  in  the 
laboratory.     It  is  by  no  means  one  of  the  rarer  mutations. 

VARIATION  OF  NOTCH. 

The  most  conspicuous  character  of  the  female  heterozygous  for 
Notch  is  the  serration  at  the  end  of  the  wings  (fig.  91)  caused  by  the 
absence  of  the  marginal  bristles  and  generally  accompanied  by  a  slight 


GENES   MODIFYING    NOTCH.  347 

concavity  of  the  edge.  The  range  of  variation  of  the  notching  is  very 
wide.  That  the  Hmit  of  variabiUty  overlaps  in  one  direction  the  nor- 
mal wing  is  certain,  for  amongst  the  daughters  without  notching  occn- 
sionally  one  is  found  half  of  whose  daughters  are  notched.  The  not 
unusual  occurrence  of  a  fly  with  one  entire  wing  and  one  with  notching 
(fig.  91,  c)  indicates  that  the  range  of  variation  includes  normal  wings. 
The  low  'productivity  of  the  Notch  female  ai)i)oars  to  be  an  incidental 
effect  of  the  Notch  factor,  because  the  normal  sist^Ts  of  the  same  stock 
are,  whenever  tested,  much  better  producers.  The  viability  of  the 
Notch  females  is  fairly  good,  but  they  appear  to  run  behind  their  nor- 
mal sisters  in  nearly  all  cultures.  Change  in  the  viability  will  be  di.^^- 
cussed  later. 

THE  PROBLEM. 

Throughout  the  older  literature  dealing  with  selection,  the  idea  tlmt 
the  grade  of  any  character  shown  by  animals  or  plants  is  a  criterion  of 
the  condition  of  the  genetic  factor  or  gene  responsible  for  the  character 
continually  recurs,  and  the  same  idea  appears  occasionally  in  more 
recent  times,  despite  Johanssen's  analysis  showing  the  inconsequence 
of  such  an  argument,  and  despite  the  accumulated  demonstrations 
that  the  production  of  a  given  character  depends  on  the  environment 
and  on  internal  modifying  genes,  as  well  as  on  the  principal  gene  itself. 
The  wide  range  of  variability  of  the  notching,  the  fact  that  the  females 
genetically  Notch  may  be  identified  by  the  2  to  1  sex-ratio  in  the  off- 
spring, even  when  the  wings  themselves  have  somatically  the  normal 
margin,  as  well  as  the  fact  that  it  is  a  dominant,  and  therefore  any 
alteration  in  the  gene  may  be  tested  directh'  by  outbreeding;  the  fact 
that  linkage  relations  made  it  possible  to  identify  any  changes  that 
might  follow  selection  in  the  individuals  that  were  Notch,  although 
with  normal  wings;  all  these  made  Notch  excellent  material  on  which 
to  put  to  actual  test  some  of  the  older  as  well  as  current  views  con- 
cerning the  nature  of  Mendelian  factors  and  the  influence  of  selection. 
In  each  generation  several  (usually  2  to  10)  virgin.  notched-winge<l 
females  (of  the  derived  type)  were  picked  out  and  put  into  a  new  bottle 
with  one  to  10  males.  Occasionally  pairs  were  used  antl  then  ma.^s 
selection  followed  in  the  next  generations.  This  prodecure  is  not  un- 
like the  rough  procedure  formerly  practised  by  the  breeder,  but  is  not, 
of  course,  to  be  recommended  for  a  thorough  understantling  of  the 
changes  that  are  taking  place  during  the  selection  jieriod.  Moreover, 
by  such  a  method  the  end  result  is  attained  only  after  a  long  time, 
whereas  the  results  here  described  could  proliably  have  been  reached  in 
two  or  three  generations;  for,  as  the  duplicate  experiments  show,  the 
modifying  gene  for  ''slight  notch"  did  not  arise  in  the  course  ()f  the 
experiment,  but  was  present  in  some  flies  of  the  stock  at  the  beginning. 


348 


GENES   MODIFYING    NOTCH. 


On  the  other  hand,  had  the  sequel  shown  that  the  results  were  due  to  a 
number  of  factors  present  at  the  beginning,  the  mass-culture  method 
would  have  offered  a  better  chance  of  collecting  the  different  modi- 
fiers in  the  same  strain.  The  object  of  the  selection  process  here  prac- 
tised was,  however,  to  produce  by  a  rough  method  results  of  the  kind 
familiar  to  the  breeder,  and  then  to  show,  by  the  refined  tests  that  the 
Drosophila  work  has  made  possible,  what  had  been  done  to  the  original 
stock 

CONDITION  OF  STOCK  BEFORE  SELECTION. 

In  table  1  there  are  records  of  the  offspring  of  11  pairs  of  Notch 
females  by  normal  males.  The  totals  give  577  Notch  females,  608 
normal  females,  613  normal  males.  It  is  clear  that  the  viability  of  the 
Notch  females  compares  favorably  with  that  of  the  normal  females. 
Very  few  of  the  Notch  flies  could  have  had  normal  wings  when  this 
class  comes  so  near  to  the  realization  of  their  expected  numbers.  How- 
ever, there  were  other  females  that  had  the  same  origin  in  which  the 
ratios  amongst  the  offspring  were  strikingly  different.  These  are 
given  here  in  table  2. 

Table  1. 


Ref. 

Notch. 

Normal   ? . 

Normal  c?. 

Ref. 

Notch. 

Normal   9  • 

Normal  d^. 

PT 

PN 

Pn 

50-1 

PN 

PN 

PN 

40 
9 
29 
40 
42 
36 
52 

49 
8 
21 
40 
46 
35 
40 

35 
9 
32 
42 
44 
27 
46 

50-1 

PN 

SvS 

45 

42 

37 

205 

51 

52 

46 

219 

60 

55 

41 

212 

50-1 

Total .  .  . 

577 

608 

613 

Table  2. 


Ref. 

Notch. 

Normal    9  • 

Normal  cf. 

Ref. 

Notch. 

Normal   9  ■ 

Normal  cf 

u 

25 
47 
35 
39 
75 

91 

77 
126 
122 
182 

36 
65 

147 
97 

172 

SSG 

SSO 

DO 

Total .  . 

89 
49 
52 

137 
115 
170 

114 

99 

106 

Pu 

ss 

'^!^ 

EVN 

409 

1,020 

836 

In  these  8  sets  the  Notch  females  are  not  half  as  numerous  as  the 
males  and  less  than  half  as  numerous  as  the  normal  females.  The 
normal  females  are  greatly  in  excess  of  the  males.  If  we  suppose  that 
here  a  considerable  number  of  the  Notch  females  have  normal  wings — 
as  was  actually  shown  to  be  the  case  later  in  the  offspring  of  some  of 
these  sets — the  discrepancies  between  tables  1  and  2  may  be  accounted 
for.    Thus,  if  we  add  the  two  classes  of  females  (1429)  and  divide  by 


GENES   MODIFYING    NOTCH.  349 

2  to  give  the  expected  number  of  Notch  females  (viz,  714),  the  results 
would  mean  that  about  300  of  the  Notch  females  had  varied  inf..  \ho 
normal  class  of  females. 

We  may  make  the  comparison  in  another  wav.  If  the  number  of 
the  males  be  taken  as  the  measure  of  each  class  of  females,  there  uill 
be  over  400  too  few  Notch  females,  and  about  20f)  too  many  nornuil 
females. 

It  was  the  offspring  of  some  of  these  lots,  viz,  the  SS  lots,  tlmt  later 
furnished  the  materials  for  selection  (SSO,  SSO  1,  etc.).  If  the  above 
interpretation  be  accepted  as  plausible,  then  at  the  beginning  of  the 
experiment  either  different  genes  for  Notch  were  present  or  modifying 
genes  were  there.  The  later  tests  proved  the  presence  of  a  modifying 
gene,  but  since  this  is  not  sex-linked,  it  may  have  been  present  in  certain 
of  the  females  or  males  either  in  heterozygous  or  homozygous  condition, 
hence,  until  the  stock  could  be  made  homozygous  for  this  gene,  random 
selection  would  be  expected  to  give  for  some  time  variable  results. 

SELECTION  OF  FEMALES  HAVING  NOTCH  IN  ONE  WING 

ONLY. 

If  the  somatic  characters  were  an  index  of  the  condition  of  the  differ- 
entiating factor  for  a  character,  it  would  appear  that  those  flies  in  which 
the  character  appeared  in  only  one  wing  should  indicate  a  change 
towards  the  phenotypic  normal  end  of  the  variation  cur\'e.  Hence  by 
selecting  in  successive  generations  as  parents  those  flies  that  had  the 
character  only  in  one  wing,  and  amongst  these  only  those  in  which  it 
was  developed  to  the  slightest  visible  extent,  then  one  might  expect  to 
bring  about  a  change,  but  of  course  this  would  be  equally  true  whether 
the  selection  was  based  on  a  changing  factor  or  on  the  more  frecjuent 
presence  of  one  or  more  modifying  factors.  An  experiment  of  this 
sort  was  begun  in  the  third  generation  aft^r  SSO  (viz,  in  SSO  H2)and 
continued  through  11  generations,  with  the  result  shown  in  the  table  3. 
In  the  first  column  are  given  the  flies  in  which  both  A\'ings  are  notched, 
in  the  second  the  flies  with  a  notch  in  only  one  wing,  in  the  third  the 
females  with  normal  wings,  and  the  fourth  the  males.  I  have  intlicated 
by  the  star  (*)  those  records  in  which  it  appears  that  a  considerable 
portion  of  the  potential  Notch  females  fall  into  the  phenotypic  normal 
class  as  shown  by  the  excess  of  normal  females  and  the  deficiency  of 
Notched  females  over  the  number  of  the  males.  This  change  is  notice- 
able in  the  sixth  to  the  eleventh  generation.  In  the  last  4  generations 
this  relation  holds  for  all  the  cultures,  with  two  exceptions  only  in  the 
eighth  generation.  It  is  probable,  therefore,  that  at  this  time  the  full 
force  of  selection  has  been  accomplished  and  there  is  nothing  to  indicate 
that  unless  some  new  sort  of  change  were  to  occur,  selection  would 
accomplish  anything  further  after  the  ninth  generation. 


350 


GENES   MODIFYING   NOTCH. 


SELECTION  OF  SOMATICALLY  NORMAL  WINGED  FEMALES 
THAT  ARE  GENETICALLY  NOTCHED  FEMALES. 

At  the  beginning  of  the  work  a  few  lines  were  run  with  eosin  ruby 
males  which  were  bred  to  the  Notch  females,  but  the  history  of  these 

Table  S.—SS  Set. 


Both 

One 

Normal 

Normal 

Gen. 

Notch 
9. 

Notch 
9. 

9. 

d". 

1 

17 

14 

88 

*63 

1 

15 

2 

18 

18 

1 

8 

7 

27 

29 

1 

Total 
2 

23 

19 

136 

*109 

63 

42 

269 

219 

9 

4 

19 

4 

2 

9 

4 

19 

4 

2 

Total 
3 

38 

14 

55 

64 

56 

22 

93 

72 

5 

1 

17 

7 

3 

12 

9 

28 

27 

3 

11 

4 

38 

*40 

3 

Total 
4 

16 

12 

49 

50 

44 

26 

132 

124 

6 

4 

42 

37 

4 

7 

4 

13 

14 

4 

15 

2 

29 

25 

4 

Total 
5 

14 

17 

29 

25 

42 

17 

113 

101 

13 

7 

24 

14 

5 

3 

10 

35 

26 

5 

16 

4 

38 

*22 

5 

4 

1 

5 

5 

5 

19 

3 

45 

*33 

5 

4 

5 

17 

17 

5 

11 

13 

52 

*24 

5 

3 

2 

6 

2 

5 

Total 
6 

6 

4 

22 

IS 

79 

49 

254 

161 

9 

4 

11 

8 

6 

3 

8 

32 

18 

G 

6 

20 

127 

*41 

f) 

3 

3 

14 

13 

(> 

6 

14 

102 

*61 

6 

5 

7 

40 

*20 

6 
Total 

1 

10 

39 

*19 

33 

66 

365 

180 

Gen. 


7 

7 
7 
7 
7 
7 
7 
7 
7 
7 
7 
7 

Total 

8 
8 
8 
8 
8 
8 

Total 

9 
9 
9 
9 
9 

Total 

10 
10 
10 
10 
10 
10 
10 
10 
10 
10 

Total 

11 
11 
11 
11 

Total 


Both 

Notch 

9. 


0 
3 
0 
0 
4 
1 
7 
0 
6 
18 
3 
1 


43 


2 
11 

7 

5 
11 

1 


37 


1 

2 
8 
2 
4 

17 

10 
16 
15 
0 
1 
5 
3 
3 
0 
3 

56 

6 

10 

8 

1 

25 


One 

Notch 

9. 


7 

8 

4 

7 

5 

15 

7 

7 

11 

12 

7 

1 


91 


15 
10 
12 
13 
5 
19 


74 


5 

9 

23 

8 
23 

68 

6 
13 
27 

4 
11 

2 
12 

8 

1 
12 

96 

19 
10 

8 
6 

43 


Normal 
9. 


35 
19 
19 
14 
15 
76 
12 
14 
31 
228 
28 
29 


520 


21 

29 
72 

104 
24 

130 


380 


45 
56 

161 
38 

105 

405 

45 
55 

149 
24 
55 

118 
65 
96 
21 
85 

713 

107 
39 
63 
50 

259 


Normal 


*9 

15 

21 

14 

12 

*29 

9 

14 

29 

*167 

*19 

*11 


349 


22 
20 

*37 
*72 
*14 
*68 


233 


*30 
*33 
*75 

*18 
*73 

229 

^^ 
*43 

*88 
*24 
*26 
*64 
*42 
*42 
*  9 
*42 

393 

*42 
*19 
*49 
*27 

137 


GENES   MODIFYING    NOTCH.  351 

lines  is  not  clear! j^  separable  now  from  those  recorded  in  the  hi8t  sec- 
tion. There  is,  moreover,  the  possibiUty  that  during  these  eiirly  exi>e- 
riments,  stock  males  of  eosin  ruby  may  have  been  introduced  at  one 
stage.  That  these  conditions  have  not  affected  seriously  the  condition 
of  the  selected  stock  as  a  whole  is  shown  by  table  4,  where  the  nunilnT 
of  normal  females  belonging  to  the  potential  Notch  class  is  as  high  in 
most  cases  as  in  the  middle  and  latter  parts  of  the  preceding  table. 

By  introducing  into  the  experiments  the  two  genes  eosin  and  ruby, 
it  is  a  very  simple  matter  to  identify  potentially  Notch  females  from 
the  other  females  with  normal  wings.  Selecting  the  former  nmke«  it 
possible  to  carry  on  the  experiment  by  breeding  in  everj-  generation 
from  those  females  that  carry  the  factor  for  Notch,  but  do  not  show  a 
notch  in  the  wing.  In  other  words,  if  the  expression  of  a  character  (its 
phenotype)  is  a  measure  of  the  major  factor  that  produces  it,  we  should 
expect  that  an  extreme  selection  of  this  kind  would  be  an  excellent  way 
of  fixing  the  factor  altered  by  selection. 

The  location  of  the  Notch  factor  had  shown  that  it  lies  in  a  region 
of  the  X  chromosome  (fig.  92),  2.8  units  from  the  arbitrary  zero-point 
yellow.  Eosin  lies  1.5  units  and  ruby  lies  7.3  units  from  yellow.  The 
distance  betw^een  eosin  and  ruby  is  therefore  a  distance  so  short  that 
double  crossing-over  never  takes  place  within  it.  If,  then,  we  use  a 
male  whose  sex-chromosome  contains  the  factors  for  eosin  and  for  ruby, 
and  a  Notch  female  having  red  eyes  {i.  e.,  the  normal  allelomor])hs  of 
eosin  and  of  ruby)  the  gene  for  Notch  in  one  X  of  the  daughters  will 
be  located  in  a  position  between  the  eosin  ruby  genes  present  in  the 
opposite  chromosome  of  the  same  daughter,  as  seen  in  figure  92. 

Now,  as  said  above,  it  would  necessitate  double  crossing-over  to  get 
the  Notch  gene  in  between  the  eosin  and  ruby  genes,  or,  in  other  words, 
double  crossing-over  must  take  place  within  these  limits  to  produce  a 
Notch  female  with  eosin  ruby  eyes.  Of  the  many  thousands  of  females 
obtained  in  the  course  of  the  experiment,  not  a  single  double  cross- 
over of  this  kind  has  been  observed. 

Single  cross-overs  have,  however,  been  recorded  in  the  expected 
numbers.  Thus  eosin  and  Notch  females,  and  eosin  as  well  as  ruby 
males  have  appeared.  It  would  of  course  be  possible  to  obtain  a  Notch 
fly  with  eosin  ruby  eyes  by  first  getting  a  single  cross-over  of  eosin 
Notch  and  then  after  mating  such  a  female  to  an  eosin  ruby  male  some 
daughters,  in  which  a  cross-over  between  Notch  and  ruby  would  result, 
having  eosin  Notch  ruby  in  the  chromosome.  Such  a  female  bred  to 
an  eosin  ruby  male  would  give  some  daughters  of  the  desired  cL'Uvs. 
As  there  was  no  need  in  my  work  for  such  females,  I  have  not  taken 
the  trouble  to  make  them. 

Turning  to  table  4,  we  see  that  nothing  further  resulted  from  select- 
ing the  potentially  normal  females  through  about  5  more  generations. 
By  potentially  normal  females  I  mean  that  females  with  red  eyes  and 


352 


GENES   MODIFYING   NOTCH. 


without  Notch  in  the  wings  were  selected.  All  red-eyed  females  must 
carry  the  Notch,  whether  they  show  the  character  or  not,  as  has  been 
explained.  At  the  end  of  the  experiment  the  relation  between  the 
Notch  and  normal  (of  two  kinds)  females  was  about  the  same  as  that 
after  a  few  generations. 

Table  A.—SS-162  Set. 


Gen. 

Both 

wings 

Notch  9 . 

One 

wing 
Notch  9  . 

Normal 

9. 

Eosin 
ruby 

9. 

Eosin 
ruby 

Eosin 

Notch 

9. 

Ruby 

9. 

Eosin 

9. 

Notch 

ruby 

9. 

Ruby 

Eosin 

Normal 

8 

9 

3 
12 

+     1 
+  18 

4 
25 

11 
53 

6 
56 

+  1 

3 

10 

12 

6 

4 

12 

12 

22 

3 

6 

13 

2 

+  22 
+     1 
+     6 
+  10 
+  24 
+  29 
+   10 
+     7 
+  24 
+     6 

18 

3 

12 

14 

27 

10 

9 

7 

23 

12 

75 
13 
30 
72 
85 
53 
17 
92 
68 
40 

69 
14 
25 
60 

76 
52 
16 
74 
58 
28 

1 

2 
2 
8 
8 
4 

1 
1 

6 

10 

1 
1+1 

1 

10 

1 

10 

10 

7 

10 

10 

1 

1 

3 

1+1 

10 

2 
1 

2 

2 

10 

10 

2 

Total 

92 

+  139 

135 

.    545 

472 

2+9 

30 

2 

18 

1 
8 

13 
2 
6 
6 

20 
1 
7 
9 
3 

+     6 
+   14 
+  24 
+     9 
+   15 
+   13 
+  28 
+     7 
+  22 
+     5 
+     4 

12 
16 
43 

9 
17 
30 
31 

2 
22 
18 
12 

24 
63 
126 
15 
49 
64 
89 
11 
50 
27 
23 

25 
42 
96 

8 
26 
68 
92 

7 
53 
18 
26 

1 
3 

1 

2 

6 

2 
1 

1 
1 

9 
1 
2 

1 

2 

1 

1 

2 

1 

Total 

12 

12 

12 

12 

12 

12 

12 

12 

76 

+  147 

212 

541 

461 

4 

1 

14 

2 

17 

15 

17 
4 
2 
7 
6 

16 
6 
2 

16 
6 
7 

19 
6 
1 
7 

13 
5 

+  46 
+     9 
+   15 
+     2 
+     4 
+     7 
+  34 
+  22 
+     2 
+  27 
+     8 
+     4 
+  50 
+     1 
+  11 
+  13 
+  11 
+     6 

48 
11 
62 
34 
18 
21 
53 
31 
17 
54 
12 
18 
87 
5 
27 
23 
22 
14 

107 
24 
83 
44 
36 
32 

131 
63 
21 

109 
38 
36 

178 
36 
22 
55 
68 
17 

100 
26 
79 
36 
44 
24 

155 
75 
20 
98 
28 
44 

137 
25 
22 
64 
58 
16 

2 

2 
1 
5 
1 
5 
4 
3 
1 

2 
1 

2 

3 
3 

4 
1 
1 

1 

3+2 

3 

1 

3 

12 

1. . 

12 

12 

1 

10 

1 
3 

1 

12 

5 
6 
2 
2 
2 

12 

2 

1 

12 

1 

12 

2 

12 

5 
1 

12 

12 

1 

Total 

155 

+272 

557 

1,000 

1,051 

3+9 

3 

50 

1 

7 

28 

GENES    MODIFYIXrj    NOTCH. 


353 


Table  4 

.— ss- 

-162  Set — continued. 

Gen. 

Both 

wings 

Notch  9 . 

One 

winK 

Notch  9  . 

Normal 

9. 

Eosin 

ruhv 

9. 

Eonin 
ruby 

cT. 

Eortin 

Notch 

9. 

Ruby 
9. 

EoBJn 

9. 

Notch 
ruby 

9. 

Ruby 

EoKtO 

d'. 

Normal 

13 

2 

1 

5 

10 

6 

6 

4 

7 
') 

1 
13 

+   16 
+     6 
+    15 
+   14 
+  41 
+   15 
+   11 
+   23 
+    13 
+     3 
+  42 

8 
19 
21 
79 

127 
31 
14 
3() 
44 
21 

114 

10 

20 

3h 

131 

131 

51 

31 

73 

62 

24 

169 

14 
14 

37 

111 

121 

34 

22 

77 

74 

25 

130 

13 

2 

1 

14-2 

1 

1 

1 
2 

1 

13 

13 

I 
1 

3 

13 

3 

13 

3 
3 

1 

13 

13 

2 

1 

13 

1 

13 

6 

13 

3 

13 

1 

10 

3 
1 

Total 

57 

4-199 

514 

740 

659 

14-10 

1 

22 

3 

14 

3 
7 
2 

11 
6 

13 
2 
4 
1 

23 

11 
2 
2 

18 

+   13 

4-   14 

4-     8 

34 

28 
17 
24 

8 
23 
54 
12 

6 
62 
37 
17 
54 
62 

50 

48 

41 

72 

17 

68 

84 

20 

14 

136 

57 

36 

102 

126 

40 
43 
35 
55 
12 
5h 
89 
19 
19 

120 
58 
38 
84 

120 



14 

4-1 

14 

14 

1 
I 
2 
1 
1 
1 
6 
1 
2 
1 
9 

14 

4-     9 
4-  24 
4-  24 
+     9 
4-     9 
4-  43 
4-  26 
4-     8 
4-   17 
4-  39 

14 

4-3 

6 
3 
3 

14 

1 

14 

14 

14 

14 

1 

14-2 

2 



1 

14 

14 

1 

14 

6 

Total .... 
15 

105 

4-243 

448 

871 

790 

14-9 

33 

2 

1 

29 

20 

11 

3 

2 

0 

0 

20 

34 

5 

-  44 

-  2)S 
4-     S 
4-     3 
4-     6 
+     6 
4-  35 
4-  30 
4-   15 
4-     4 
4-     4 
+     1 

21 
25 
23 

5 
30 
30 
21 
51 
()4 
33 

6 
12 

3 
21 

77 
72 
69 
12 
23 
23 
77 
127 
95 
25 
26 
27 
8 
54 

79 
76 
63 

4 
11 
12 
80 
102 
64 
33 
12 
12 

8 
39 

5 
10 
10 

1 

2 

3 
3 
3 

15 

15 



15 

4-1 

15 

15   .    . 

15 

6 

1 

2 

3 

11 

4 

1 

1 

15 

3 
6 
1 

15 

15 

15 

3 

4-1 

15 

15.  .  . 

1 
3 

15 

1 

4-     3 

Total 

16 

99 

4-187 

345 

715 

493 

4-9 

36 

4 

32 

4 

3 

13 

6 
2 
2 
0 

7 
6 

+  37 
-f   17 
+   13 
4-     3 
4-  32 
4-  22 
+     3 
+     2 

46 

58 

61 

6 

34 

117 

4 

4 

74 
102 
77 
10 
83 
144 
10 
24 

65 
86 
71 

9 

85 

138 

5 
25 

7 
2 

6 

16 

16 

14-1 

1 

16 

16 

1 
1 

1 

11 

1 
1 
7 

1 

1 
3 

16 

16 

16 

2 

Total 

25 

4-129 

330 

524 

484 

14-3 

1 

35 

2 

24 

354 


GENES   MODIFYING   NOTCH. 


Table  4. 

SS- 

-162  Set — continued. 

Gen. 

Both 

wings 

Notch  9  . 

One 

wing 

Notch  9  . 

Normal 

9. 

Eo.sin 
ruby 

9. 

Eosin 
ruby 

Eosin 

Notch 

9. 

Ruby 

9. 

Eosin 
9. 

Notch 
ruby 

9. 

Ruby 

Eosin 

Non 

17 

17 

3 

1 

22 

12 

5 

+  13 
+  3 
+  11 

+  24 
+  20 
+  6 

24 

6 

21 

119 

31 

4 

72 
IS 
31 
160 
55 
11 

71 
15 

27 

171 

50 

10 

+2 

8 
1 
2 

7 

9 

17 

17 

17 

1+1 

1 

2 

4 
1 
1 

17 

17 

1 

5 

Total 

18 

53 

+  77 

205 

297 

344 

1+4 

1 

23 

2 

15 

3 

+  3 

+  5 
+  35 
+  28 
+  33 
+  29 
+  13 
+  48 
+  2 
+  9 
+  1 

12 
30 
75 
36 
51 
26 
20 
103 
11 
15 
6 

20 

47 

109 

106 

110 

65 

77 

194 

20 

25 

7 

16 

24 

95 

113 

85 

69 

59 

217 

18 

28 

2 

18 

1 

8 
10 

7 



18 

15 
8 

13 

14 
6 

24 

3 
1 

2 

1 

1 
6 
3 
2 

1 
9 
1 

18 

18 

18 

1 

1 

18 

6 
9 

18 

1 

1 

18 

18 

1 

18 

Total 

19 

84 

+206 

385 

780 

726 

6 

1 

41 

4 

23 

+  5 
+  4 
+  2 
+  5 

18 

18 

15 

6 

5 

20 

21 

36 

6 

30 

17 
45 
14 
15 
11 
28 
25 
65 
45 
135 

21 
26 
12 
25 
8 
33 
24 
64 
34 
144 

+  1 

1 
2 
2 
1 

1 
1 

19 

1 

19 

1 

19 

1 
1 

19 

19 

+  2 
+  3 
+  IS 
+  7 
+  25 

19 

2 

19 

5 

11 
o 

1 
3 

4 

19 

1 

2 

19 

5 



Total .... 
20. 

21 

+  71 

175 

400 

391 

+3 

16 

2 

11 

2 
3 
6 

7 
2 

+  2 

+  1 
+  5 
+  18 
+  20 
+  3 

11 

7 
14 
42 
28 
14 

51 
S 
43 
59 
62 
26 

37 
7 
43 
61 
39 
9 

+  1 

7 

2 

20 

20 

20 

2 
1 

1 

2 
2 
3 
1 

2 

4 
2 

2 

1 

20 

20 

1 

Total 

21 

21 

21 

21 

20 

+  49 

116 

249 

196 

+5 

15 

1 

12 

4 
2 
2 
1 

+  6 
+  18 

+  8 
+  8 

15 
14 
35 

17 

28 
31 
74 
45 

25 
33 

71 
50 

1 
1 
4 

1 

2 

1 
3 

1 

Total 

22 

23 

9 

+  40 

81 

178 

179 

1 

6 

1 

6 

21 

+  25 

27 

68 

64 

1 

5 

1 

+  3 

+  17 

13 
17 

24 
51 

26 
55 

23 

Total 

24 

24 

Total 

8 

8 

1 

8 

+  20 

30 

175 

81 

8 

1 

1 
4 

+  5 
+  16 

12 
20 

8 
47 

11 
36 

1 
1 

1 
3 

5 

+  21 

38 

55 

47 

2 

4 

GENES   MODIFYING    NOTCH. 


35.J 


DUPLICATE  SELECTION  EXPERIMENT. 
At  the  time  when  the  former  series  began  another  set  (X  6  set)  was 
started  and  kept  apart  from  the  former.     From  the  third  to  the  ninth 
generation,  as  shown  in  table  5,  females  tliat  had  Noteh  in  only  one 

Table  5.— X  6  Set. 


Gen. 

Both 

wing.s 
Notch    9. 

Ono 

winK 

Notch    9. 

Normal 
9 

Eosin 

ruby 

9. 

Eoain 
ruby 

Eosin 

Notch 

9. 

Ruby 
9. 

Eoain 
9. 

Notch 

ruby 

9. 

Ruby 

d". 

Eodn 

Normal 

0 

1 

+   14 
+     5 

04 

45 

2 
21 

42 

3 

» 

1 

+   19 

109 

23 

42 

Total 

10 
1 
1 
3 

1 

+     8 
+     9 
+     4 

+     7 

52 

30     1     47 

6 

42 

26 

40 
48 
5 
12 
37 

142 

7 

Total. 

16 

+  28 

203 

7 

26 
13 

7 
2 
8 

5           

8 

7 

1 

2 

1 

9 

11 

2 

3 

7 

1 

4 

7 

13 

14 

3 

21 

10 

4 

0 

0 

13 

14 

2 

+     9 

4-     1 
+     4 
+     1 
+     4 
+  11 
+     5 
+     6 
+     8 
+     3 
+     6 
+     6 
+     8 
+     8 
+   12 
+     6 
+     5 
+  19 
+     5 
+     4 
+   12 
+     8 
+  12 
+     4 

16 
30 
22 

1 
10 
42 
37 

5         .... 

5 

5 

5 

1 
22 
21 

6 
21 

2 

5 

a, 

2 
2 

1 

5 

2 
3 
6 
14 
31 
28 
28 
37 
75 

7 

12 

22 

9 

5 

5 

13 

2« 
23 

) 

• 

5 

) 

'29" 
42 
16 

20 

3 

46 

28 

30 

9 

5 

) 

) 

} 

) 

\ 

36 

28 
37 
16 

io 

20 
13 



1 

7 

Total. . . . 

157 

+  167 

fi'^R 

221 

4 

166 

10 

13 

9 

10 

25 

2 

1 
7 
5 
5 
0 

+   13 
+   11 

4-     5 
4-  30 

4-     2 

25 
52 

4 

187 

10 

1 

11 

"24 

55 

12 

2^ 

IDS 

144 

35 

17 
44 
26 

88 
8 

7 
33 
12 

4 
27 
23 

"+"2" 

4-     1 
4-     7 
4-     8 
4-     2 
+     1 
+   28 
+    17 

15 
60 
0 
25 
85 
141 

2 
26 
53 

Total. . . . 

158 

4-127 

661 

87 

141 

428 

356 


GENES   MODIFYING   NOTCH. 


Table  5. — X  6  Set — continued. 

Gen. 

Both 

wings 

Notch  9. 

One 

■Rang 

Notch  9. 

Normal 

Eosin 

ruby 

9. 

Eosin 
ruby 

Eosin 

Notch 

9. 

Ruby 

Eosin 

9. 

Notch 
ruby 

9. 

Ruby 

Eosin 

Non 

7 

3 

1 

34 

16 

16 

2 

17 

17 

45 

5 

7 
4 

+     1 
+     2 
+   12 
+     7 
+   10 

20 
13 
62 
39 
55 

7 
36 
67 

4 
82 

20 

?: 

7 

5 

1 

7 

5 

7 

4J 

7 

^ 

7 

4 

7 

+     6 
+     2 
+  17 
+  24 

+      1 
+     6 

7f. 

7 

.... 

41 

7 

82 

71 

1 

7 

3: 

7 

7 
16 

5 

27 

7 

1 

1 

Total. . . . 
8 

167 

+  88 

405 

110 

107 

1 

2 

26' 

14 

3 

12 

6 

20 

13 

15 

8 

+  17 
+     9 
4-  29 
+  16 
+  39 
+     3 
+   14 
+  24 

4 
47 
98 
50 
34 

5 
79 
41 

42 

8" 

72" 
24 

66' 

35 
3 

2 

5 
7 
3 

8 

8 

8 

4 
79 
19 

1 

78 

8 

8 

2 
1 

2 

6 

8 

8 

1 

Total. . . . 
9 

91 

+  151 

358 

212 

219 

1 

7 

22 

15 

5 

13 

4 

3 

17 

14 

3 

30 

41 

8 

13 

8 

8 

4 

+     4 
+     5 
+  13 
+     2 
+   16 
■+     7 
+  16 
+  15 
+  14 
+  15 
+     6 
+  16 
+     6 
+   12 
+   15 

4 

5 
46 
13 

7 
14 
22 
16 
10 
23 

8 
12 

9 
10 
16 

23 
21 

26 
17 

1 

1 



9 

9 

4 

9   . . 

37 
44 
36 
53 
16 
35 
88 
29 
56 
20 
18 
45 

31 

29 
37 
57 
30 
57 
84 
28 
50 
14 
13 
61 

1 

2 
1 
3 

1 

3 
1 

1 
2 

1 

9.  .  . 

2 

9 

9 

1 

1 
2 
2 

9 

9 

9 

4 

2 

4 

9 _. 

9 

5 

1 

8 
1 



9 

9   . 

9 

1 

1 

1 

Total. . . . 
10 

186 

+  162 

215 

521 

534 

6 

7 

9 

4 

8 

21 

I 

6 
4 

+   15 

+  20 

11 
13 

42 
39 

45 

1 

1 

1 

1 

10 

1 

Total. . . . 

10 

35 

24 

81 

46 

1 

1 

1 

1 

1 

6 

13 

2 

2 

9 

3 

12 

40 

13 

+     1 
+   13 
+  23 
+     8 
+     6 
+   13 
0 
+  46 
+  22 
+   11 

2 
21 
16 
15 
14 
30 
22 
84 
7 
8 

16 
42 
48 
18 
16 
70 
49 
158 
57 
32 

18 
33 
46 
17 
20 
40 
41 
167 
52 
27 

1 
8 
3 

2 
3 
0 
1 
1 
2 
2 
4 

2 
1 

5 

1 
1 

1 

3 

8 

1 

Total. . . . 

101 

+  143 

219 

406 

361 

4 

3 

26 

2 

15 

1 

GENES   MODIFYING    NOTCH. 


3r)7 


Table  5.—X  G  Se^— continued. 


Gen. 

Both 

wings 

Notch    9 

One 
wing 
.  Notch    9 

Norma 

Eosin 

ruby 

9. 

Eosin 
ruby 

Eosin 

Notch 

9. 

Ruby 

9. 

Eoniii 
9. 

Sotch 

ruby 

9. 

Ruby 

EoMO 

.N'ormal 

> 

13 
21 
16 

8 

+  17 
+  79 
+  25 
+   12 

7 

123 

33 

7 

55 

172 

72 

19 

23 

178 

70 

24 

4 

18 
1 
2 

I 

1+1 

1 

11 

4 
1 

J 

Total. . . . 
i 

58 

+  133 

170 

318 

42 

8 

10 

295 

1+1 

25 

I 

10 

15 
3 

7 

+    10 

+      1 

+      1 

17 

34 

8 
12 

1 

1 

5 

..... 

2 

i 

\ 

Total. . . . 

25 

+  12 

17 

60 

54 

1 

1 

6 

2 

+     5 
+     1 
+   11 
+     4 
+     7 
+   12 
+  23 
+     6 
+    18 
+   11 
+  20 

5 

1 

17 

1 

8 

20 

21 

24 

12 

11 

17 

12 

5 
24 

9 
13 
21 
57 
66 
104 
28 
50 

13 

7 
23 

4 
13 
24 
65 
38 
87 
27 
50 

1 

3 

4 

3 

4 

6 

6 

12 

14 

6 

10 

1 



1 

1 
I 

1 
3 

I 
1 

1 

+2 

1 
2 

8 

2 

1 

8 

10 

Total. . . . 

68 

+  118 

137 

389 

351 

+3 

9 

14 

2 

12 

6 



+     2 
+     4 
+     6 
+    13 
+   14 
+   13 
+    19 

8 
6 
16 
12 
9 
15 
52 

18 
22 
17 
14 
29 
27 
69 

30 
20 
18 
10 
18 
24 
80 

2 

7 
3 
8 
1 
14 

1 
1 
2 

1 

1 

1 

1 
1+3 

•> 
1 

Total. . . . 

35 

+  71 

118 

196 

200 

1+5 

3 

1 

5 

=^ 

17 
3 

17 
10 

+  29 
+     3 
+    11 

+      <i 
+     9 
+      1 

+    n 

+    « 

+     5 
+  78 

56 

5 

12 

10 

16 

18 

10 

12 

4 

143 

63 
10 
37 
36 
21 
14 
35 
19 
17 
252 

59 

3 

36 

31 

13 

18 

22 

22 

S 

212 

16 

1 

5 

1 
1 

1 

1 

1 
I 

2 
11 

7 
3 

1 
3 

3 

o 

22 

2 

9 

Total. . . . 

70 

+  156 

286 

504 

424 

4 

44 

4 

18 

wing  were  chosen  as  parents.  Progress  was  slow,  but  there  are  clear 
indications  at  the  end  that  the  stock  was  ditTerent.  I  .it  t  le  i)r()gr(\'<s  was 
made  until,  during  the  eighth  generation,  the  i)lien()typic  normal 
females  were  used  as  parents.  From  the  ninth  to  twelfth  generation 
inclusive  a  marked  addition  to  the  phenotypic  normal  chiss  became 
evident  in  most  of  the  cultures.  At  the  end  of  the  selection,  males  of 
this  stock  were  bred  to  females  of  the  other  selecteil  line  (8S,  102). 


358 


GENES   MODIFYING   NOTCH. 


Had  different  modifying  factors  been  present,  the  atavistic  type  of 
Notch  should  have  been  shown  by  the  daughters,  but  if  both  Hues  had 
been  changed  through  the  isolation  of  the  same  modifying  gene,  the 
results  are  expected  to  be  the  same  as  when  the  male  comes  from  the 
same  line  as  the  Notch  female.  The  cross  showed  that  the  Notch 
modifier  was  the  same  in  both  lines. 

LOCALIZATION  OF  THE  GENE  FOR  NOTCH. 

Earlier  evidence  had  shown  that  the  gene  for  Notch  lies  in  the  X- 
chromosome  somewhere  in  the  region  between  eosin  and  ruby.  The 
following  "three  point"  experiment  was  devised  to  furnish  more  precise 
data.  The  red-eyed  Notch  female  was  bred  to  an  eosin  ruby  forked 
male.  Her  Notch  daughters  are  expected  to  contain  one  X  chromosome 
with  the  Notch  locus  and  the  other  X  chromosome  to  contain  the  eosin 
ruby  forked  loci.  The  approximate  location  of  these  loci  is  that  shown 
in  figure  92. 

The  figure  also  indicates  that  three  possible  regions  of  crossing  over 
occur  between  the  three  pairs  of  genes  involved.  There  are  sixteen 
possible  classes:  two  non-cross-overs,  six  single  cross-overs,  six  double 
cross-overs,  and  two  triple  cross-overs.  The  characters  shown  by  each 
of  these  classes  are  the  following : 


Non-cross-overs 


1.  eosin  ruby  forked 

2.  Notch 


Single  cross-overs  Double  cross-overs  Triple  cross-overs 


1.  eosin  Notch. 

2.  ruby  forked. 

1 

3.  eosin. 

4.  Notch  ruby  forked. 

1.  eosin  Notch  ruby  forked. 

2.  wild  tj-pe. 


1.  eosin  Notch  ruby. 

2.  forked. 


3.  eosin  Notch  forked. 

4.  ruby. 


5.  eosin  ruby. 

6.  Notch  forked. 


5.  eosin  forked. 

6.  Notch  ruby. 


When  an  Fi  Notch  of  this  composition  is  crossed  to  an  eosin  ruby 
forked  male  (the  multiple  recessive)  all  the  classes  of  gametes  produced 
by  such  a  female  will  be  revealed  both  in  the  female  and  in  the  male 
offspring,  except  that  there  \Adll  be  only  half  as  many  classes  of  males 
as  of  females,  since  all  those  males  that  get  the  gene  for  Notch  will  die. 
In  the  table,  the  male  classes  are  entered  separately  from  the  female 
classes.  It  was  anticipated  that  calculations  based  on  the  males  alone 
would  be  more  accurate  than  those  based  on  the  females  alone,  because 
in  the  latter  sex  there  is  some  difficulty  in  separating  the  eosin  from 
the  ruby  females,  while  in  the  males  no  such  confusion  is  possible.  The 
computations  show,  however,  that  the  differences  between  the  two 
sets  of  data  are  as  near  as  is  to  be  expected  for  the  numbers  involved. 
Therefore  the  estimates  based  on  the  total  figures  are  probably  to  be 
preferred. 


ff 


GENES   MODIFYING    NOTCH. 


359 


X 
X 


■"*y 


X 


There  is  a  small  chance  of  contamination  from  tho  food  when  so 
many  cultures  as  these  are  carried  out,  even  althouj^h  all  tho  ordinary 
precautions  are  taken.  Thus  the  four  normal  males  that  apixuircil  are 
under  suspicion.  Tvvo  of  these  were  tested  to  the  second  generation 
and  found  to  contain  no  other  than  normal  j^ene.^.  Since  the  male  con- 
tains only  one  sex-chromosome,  it  was  to  be  anticipated 
that  such  red-eyed  normal  males  would  not  contain  any 
other  sex-linked  genes  than  they  show  unless  something 
unusual  had  occurred.  It  is,  however,  conceivable  that 
a  lethal-bearing  male  rarely  comes  through  (as  happens 
in  the  case  of  a  few  other  lethals)  even  although  no  n(»t('h 
is  observable  in  the  wing.  Were  this  possible  some  of  his 
daughters  or  granddaughters  would  be  expected  to  sht)w 
Notch,  but  as  none  did  so,  the  presumption  is  that  these 
red-eyed  males  were  not  of  this  kind.  It  is  also  possible 
to  mistake  at  times  an  old  ruby-eyed  fly  for  a  red-eyed  fly 
if  only  a  casual  examination  is  made,  but  as  it  was  appre- 
ciated that  no  red-eyed  male  was  expected,  a  careful 
scrutiny  of  the  red  males  was  made.  For  these  and 
other  reasons  I  have  discarded  the  two  untested  males  of 
the  four  from  the  general  calculation  in  locating  the  fac- 
tors, although  I  have  also  given  the  calculations  in  which 
these  are  included.  The  differences  in  the  two  results  are 
too  small  to  be  of  significance. 

A  similar  doubt  arises  about  the  corresponding  double 
cross-over  classes  in  the  females  that  gave  two  eosin  Notch 
ruby  forked  females  and  two  normal  females.  Both  of 
the  latter  were  tested  w^th  eosin  ruby  forked  males  and 
gave  normal  sex-ratios  and  no  Notch  daughters.  All  the 
daughters  and  sons  had  red  eyes.  For  these  three  reasons  there  can  be 
little  doubt  that  both  of  these  females  in  question  were  due  to  con- 
tamination by  wild-type  flies. 

The  other  two  daughters  can  not  be  so  easily  ds missed,  because 
they  were  obviously  not  due  to  contamination,  since  they  showed  all 
of  the  genes  involved  in  the  experiment.  Unfortunately  I  ha\'e  no 
records  to  show  whether  they  were  tested,  or,  if  so,  whether  they  lived. 
It  is  true  that  occasionally  flies  are  found  that  liave  a  nick  in  their 
wings  due  to  accident  or  to  some  other  mutation,  and  in  numbers  ;is 
large  as  those  here  employed,  the  occurrence  of  such  flies  is  to  be 
expected.  It  is  to  be  regetted  that  I  was  not  aware  of  the  fact  tliat 
Notch  flies  (even  those  phenotypically  normal  for  wing  margin)  can  be 
identified,  under  the  microscope,  by  the  thicker  second  and  fifth  veins. 
B}'-  this  means  the  two  normal  eosin  notch  ruby  forked  females  eould 
have  been  securely  identified,  ^\^lile  it  is  highly  probable  that  the 
same  difference  holds  for  the  selected  notch,  this  lias  not  been  deter- 


Fni.  92. 


360 


GENES   MODIFYING   NOTCH. 


Table  6. 


Females. 

Males. 

Not 

eosin. 

Eosin. 

Not  eosin. 

Eosin. 

Not  Notch. 

Notch. 

Not  Notch 

Notch. 

Not  Notch. 

Not  Notch. 

Not 
ruby. 

Rul 

)y- 

Not 
ruby. 

Ruby. 

Not 
ruby. 

Ruby. 

Not 
ruby. 

Ruby. 

Not 
ruby. 

Ruby. 

Not 
ruby. 

Ruby. 

Not 
f. 

f. 

Not 
f. 

f. 

Not 
f. 

f. 

Not 
f. 

f. 

Not 
f. 

f. 

Not 
f. 

f. 

Not 
f. 

f. 

Not 
f. 

f. 

Not 
f. 

f. 

Not 
f. 

f. 

Not 
f. 

f. 

Not 
f. 

f. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

1 
1 
1 

1 

41 
44 
50 
20 
30 

8 
36 
37 
21 
13 
24 
14 
18 

5 
23 

4 
10 
10 
51 

6 
27 
20 

4 
12 

8 

5 
19 

5 

29 
30 
37 

14 
24 

4 
21 
29 
17 

9 
16 

6 
11 

8 
19 

3 
13 
18 
17 

5 
32 
11 

7 
15 

2 

7 

15 

4 

0 
1 
1 

1 
0 
0 

4 
2 
2 
1 
1 

0 
1 
1 
0 
0 

27 
32 
28 
19 
41 

7 
34 
26 
20 

6 
19 
11 

6 

2 
20 

4 
17 
16 
39 

8 
23 
12 

5 
14 
13 

8 
13 

6 

37 
63 

2 
3 

2 
1 

39 
35 
19 
13 

26 

3 

26 

24 

19 

6 

19 

9 

6 

2 

16 
10 

3 
21 
31 

4 
16 
11 

7 
12 
10 

3 
19 

4 

31 
50 
49 
21 
42 

8 
30 
22 
30 
21 
19 
10 
10 

4 
24 
10 
11 
21 
47 
17 
37 
16 
26 
21 
10 

5 
31 

1 

1 
1 

1 

0 

0 

1 

1 

0 

0 

41 
20 
37 

7 
25 
42 
17 
15 
14 

7 
11 

5 
26 

5 
22 
15 
47 

9 
28 
13 
21 
32 
10 

7 
16 

6 

0 

1 

0 

1 

4 
0 

2 

0 

0 

1 

1 

0 

2 

1 
3 

2 

1 
0 

1 

3 

0 

1 
0 

0 

1 

0 

1 

0 
0 
0 

2 
1 
1 

0 
2 
1 

1 
0 
0 

0 

1 

0 

0 

3 

2 

0 

2 

1 

1 

1 

0 
0 

0 

1 

0 
0 
0 
0 

0 
0 
0 
0 

1 

0 
2 
0 
2 
1 
1 
4 
5 

0 
0 
0 
0 

1 

0 
0 
2 

1 

0 

1 

2 
2 

1 
1 
0 

0 
0 

1 

1 

1 
3 
3 

0 
4 

1 

2 
0 

1 
1 

0 
0 
0 
0 

0 

0 

1 

] 

1 

0 
0 
0 

1 
1 

2 
0 
1 

0 

1 

1 
0 

0 
2 

0 
0 

1 

1 
0 

1 

1 
2 
0 

1 

0 
0 
0 

1 

1 

3 
1 

1 
3 

1 
0 

1 
1 

1 

0 

0 

1 

2 

0 

2 

13 

571 

423 

6 

15 

36 

12 

476 

598 

6 

5 

2 

4 

1 

1 

9 

33 

14 

413 

624 

mined,  because  the  original  stock  of  Notch  was  allowed  to  die  out,  and 
the  new  Notches  that  have  since  appeared  are  not  certainly  the  same 
Notch.  The  new  Notches  so  far  as  tested,  appear  to  be  deficiencies. 
(See  Mohr,  0.  L.,  1919,  Genetics,  in  press.) 

There  were  two  classes  in  the  males  where  crossing-over  occurred 
between  eosin  and  Notch  containing  9+14  =  23  cross-overs  (omitting 
2+2  =  4  double  cross-overs  discussed  above).  Dividing  these  23  by 
the  total  number  of  males,  viz,  1,095,  gives  2.1  per  cent  of  crossing- 
over.  If  the  four  questionable  individuals  are  utilized  the  result  is 
2.4  per  cent. 

There  were  two  classes  in  the  males  where  crossing-over  took  place 
between  Notch  and  ruby,  containing  33  +  1=34  cross-overs  (omitting 
the  four  individuals  as  before) .     Dividing,  then,  34  by  the  total  number 


GENES    MODIFYING    NOTCH.  301 

of  males,  1,095,  gives  3.1  per  cent  of  cros.sinR-ovor.     (If  the  four  (jiics- 
tionable  individuals  are  utilized  the  result  is  3.4  per  cent.j 

There  were  three  classes  in  the  males  where  crossing-over  occurred 
between  Notch  and  forked,  containing  413  +  14-f  1  =428  cross-overs 
(omitting  the  questionable  classes).  Dividing  the.se  by  the  total 
number  of  males,  1,095,  gives  39.1  per  cent  of  crossing-over. 

In  the  females  there  were  two  cla.sses  where  crossing-over  occurred 
between  eosin  and  Notch,  19  +  7  =  26  (omitting  the  rejected  clii.s.s(-s). 
Dividing  26  by  the  total  number  of  fenuiles,  viz,  2,125,  gives  1.2  i>er 
cent  of  crossing-over. 

In  the  females  there  were  two  classes  where  crossing-over  occurred 
between  Notch  and  ruby,  containing  51 -f  18  =  69  cross-overs  (omitting 
the  rejected  females).  Dividing  these  69  by  the  total  number  of 
females,  viz,  2,125,  gives  3.25  per  cent  of  crossing-over. 

In  the  females  there  were  three  classes  where  crossing-over  occurred 
between  Notch  and  forked,  viz,  859-1-18  +  7  =  884.  Dividing  the.se  by 
the  total  number  of  females,  viz,  2,125,  gives  41.6  per  cent  of  crossing- 
over. 

THE  IDENTIFICATION  OF  THE  MODIFYING  GENES. 

The  following  method,  which  has  come  into  use  in  this  laboratory 
as  the  best  and  quickest  method  to  identify  modifying  genes  in  the 
second  or  third  chromosome,  takes  advantage  of  two  dominant  genes, 
one  in  each  of  these  chromosomes,  as  well  as  of  the  fact  that  there  is  no 
crossing-over  between  the  members  of  any  pair  of  chromosomes  in  the 
male. 

The  three  chromosomes  of  the  Notch  female  that  are  in\-ol\'ed  are 
represented  in  the  left  top  line  in  figure  93.  The  gene  for  Notch  is  in 
one  X  chromosome  and  the  genes  for  eosin  and  ruby  in  the  other  X. 
The  second  and  the  third  chromosomes  are  supposed  to  carry  the 
modifying  gene  or  genes,  whose  presence  there  this  experiment  is 
designed  to  test. 

The  chromosomes  for  the  Star  Dichaete  (S'  D')  male  are  shown  in  the 
second  line.  The  X  chromosome  carries  only  normal  genes,  while  the 
second  chromosome  carries  the  gene  for  Star  (S')  in  one  member  of  the 
pair  and  its  normal  allelomorph  in  the  other  member;  the  thin!  chromo- 
some carries  the  gene  for  Dichaete  in  one  member  of  the  pair  and  its 
normal  allelomorph  in  the  other.  Neither  Star  nor  Dichirte  are  \i:il)le 
in  homozygous  condition;  hence,  as  stated,  one  member  of  each  of  the 
pairs  of  chromosomes  that  carry  these  dominant  genes  is  Star  or 
Dichaete  respectively,  the  other  normal. 

Therefore,  when  such  a  male  is  crossed  to  the  selected  Notch  fenmle, 
all  the  Star  Dicha;te  sons  have  received  the  Star  and  Dicluete  g(Mies 
(and  their  respective  chromosomes)  from  the  father  and  the  homologous 
chromosomes  from  the  mother.     The  single  X  chromosome  that  the 


362 


GENES   MODIFYING   NOTCH. 


male  gets  is  the  eosin-mby-bearing  X  chromosome  of  the  mother  (the 
other  males  die).  In  other  words,  their  composition  is  that  represented 
in  the  third  line  to  the  left  in  figure  93. 


1 


ReaNotcli  . 
eosin  ruby 


X 


n 


StarDichael* 


S' 


m 


D 


StarDicliaetc  J- 


S' 


D 


X 
X 


X 


D 


Fig.  93. 

If  this  male  is  now  back-crossed  to  a  selected  Notch  female  (see  figure 
93)  any  red-eyed  Notch  daughter  that  is  also  Star-Dichsete  (upper  line 
to  right;  No.  1)  must  have  gotten  the  Star  (II)  and  the  Dichsete  (III) 
chromosomes  from  her  father  (neither  of  which  bears  the  modifiers 
sought  for)  and  an  X  chromosome  also  from  the  father  with  genes  for 
eosin  ruby  eyes  and  normal  wings.  She  must  also  have  gotten  the 
second  and  third  chromosomes  that  may  carry  in  one  or  in  both  the 
modifiers  sought  for  (which  are  recessive)  from  her  mother,  as  well  as  an 
X  chromosome  bearing  the  genes  for  red-eye  and  Notch  wing.  Hence 
such  a  female  should  be  atavistic  Notch,  because  either  the  S'  or  D' 
genes  will  bring  in  the  normal  allelomorph  of  the  postulated  modifiers 
in  II  and  III.  Conversely,  females  that  are  not  Star  and  not  Dichsete 
(No.  2)  should  be  of  the  selected  type,  since  their  second  and  third 
chromosomes,  one  or  both,  contain  the  modifiers. 

Continuing  the  analysis,  it  is  evident  that  if  the  modifier  (one  or  more) 
is  in  the  second  chromosome,  then  all  Star  Notch  daughters  (No.  3) 
should  be  atavistic,  and  all  not-Stars  (No.  4)  the  selected  type  of 
Notch;  and  if  the  modifier  is  in  the  third  chromosome,  then  all  Dichsete 
Notch  daughters  should  be  atavistic  (No.  4)  and  all  not-Dichsete  (No.  3) 
selected  type  of  Notch. 

The  ability  to  pick  out  atavistic  flies  from  selected-type  flies  is  essen- 
tial to  this  test.  In  general,  this  can  be  done  successfully,  with,  how- 
ever, a  margin  of  error,  but  the  error  is  expected  from  the  information 
at  hand  to  be  so  small  as  not  to  effect  the  main  result.  Moreover,  the 
occurrence  of  red-eyed  females  with  normal  wings  (flies  that  are  known 
from  the  Hnkage  relations  of  the  experiment  to  have  the  Notch  gene) 
in  any  of  the  classes  named  above  is  an  almost  certain  index  of  the 
occurrance  of  the  modifier. 


GENES   MODIFYIN(;    NOTCH. 


363 


The  results  of  such  a  test  are  given  in  table  7.  The  tai)le  inciudejj 
only  females  and  only  the  red-eyed  females  (the  flies  tluit  are  gcriet- 
ically  Notch),  while  the  eosin  ruby  females  and  all  of  the  iruiles  were 
thrown  away.  Examination  of  the  table  shows  tluit  practically  all 
of  the  not-Star,  not-Dichaete  females  have  norniiil  wings  rpotontially 

Table  7. 


Not  star  9 . 

Star  9. 

Not-Dichsete. 

Dichsete. 

Not-Dichffite. 

Dichjcte. 

Notch 
Sel'od. 

Norm. 
Scl'cd. 

Ata- 
vistic. 

Notch 
Sei'ed. 

Norm. 
Sd'ed. 

Ata- 
vistic. 

Notch 
Scl'cd. 

Norm. 
Scl'.-d. 

At4l- 

viMtir. 

Note), 
Scl'H. 

Norfii. 
Scl'cd. 

At»- 
viHtic. 

A... 
A... 
A".. 
A".. 
A\.. 
A'... 
Ai>.. 
A".. 

A^. 

B ... 

2+1 
1+2 
1+4 
1+1 
+2 
3+1 
1+1 
2+4 
5+7 

6 
5 
7 
6 
o 
5 

9 
1 
8 

10 
5 
5 
4 

18 
7 
1 

13 

+2 
+2 
+  1 

+  1 
+  1 

+  1 
+  1 

2+2 
+  1 
+5 

1 
+2 
+2 

2+2 

1+5 
+  1 

1 
7 
s 
6 
3 
7 
3 
27 

1 
G 
2 

9 
4 
8 
17 
6 
2 

7 

6 
13 
12 

3 
10 

2 
IH 

9 

6 
16 

3 
14 

4 
27 
IH 

5 

3 

+  1 

2 

+  1 

•   ••■.. 

22 
2 

3 

4 

+3 

1 



c... 

D... 

2+6 



2 

E... 
F... 
H... 
K... 
P... 
P"... 

1+6 

+4 

3+7 

4+8 
+3 

+5 

4 
5 
11 
19 
3 
7 

9 
f. 

27 
18 

+2 
1 

1 

11 

26+62 

112 

1 

+  1 

2 

152 

6+29 

122 

4+6 

176 

Notch). ^  This  is  the  class  that  contains  the  orip:inal  second  and  third 
chromosomes  and  their  modifying  genes  if  such  were  j^resont.  Con- 
versely, practically  all  of  the  Star-Dichaete  females  are  atavistic,  and 
this  class  contains  the  Notch  females  that  have  received  the  second 
and  the  third  chromosomes  from  the  Star-Dicha^te  males.  Thus  far 
the  evidence  shows  that  the  change  that  took  place  during  selection  is 
caused  by  something  in  one  or  the  other  or  both  of  these  two  clironio- 
somes.  Whether  both  or  only  one  is  shown  by  further  analysis  of  the 
results.  For  instance,  the  fact  that  all  the  Dicha'te  flies  are  atavistic, 
and  the  fact  that  all  not  Dichsete  are  selected  type,  shows  that  the 
modifier  is  in  the  third  chromosome.  Had  the  modifying  gene  or 
genes  been  in  the  second  chromosome,  then  all  Star-<»yed  females 
should  be  atavistic,  which  they  are  not,  and,  conversely,  all  not -Star- 
eyed  females  should  be  selected  type,  which  they  are  not.  Hence 
the  modifier  in  question  is  not  in  the  second  chromosonu'. 

Finally,  the  same  evidence  proves  that  the  modifiers  that  caused 
the  change  are  not  in  the  sex  chromosome  as  recessive  modifiers  be- 

Un  this  table  (also  in  tables  4  and  5)    the  +  sign  indicates  that  the   uumlicr  of  flic*  that 
follow  were  notched  in  only  one  wing. 


364 


GENES   MODIFYING   NOTCH. 


cause  the  not-Star  not-Dichsete  females  are  practically  all  the  selected 
type,  and  the  Star-Dichsete  are  practically  all  classified  as  atavistic; 
yet  the  females  of  both  classes  contain  the  same  Notch-bearing  chromo- 
some that  must  be  identical,  since  in  both  it  is  the  X  chromosome  of 
the  selected  stock. 

In  the  Fi  generation  (table  8),  the  parents  of  the  flies  in  table  7,  it  was 
found  that  all  of  the  Notch  females  were  atavistic  as  expected.  In 
some  sets  the  extent  to  which  notching  was  developed  was  greater 
than  in  others.  It  is  important  for  present  purposes  to  note  that 
there  is  no  difference  in  the  extent  of  development  of  the  character 
Notch  in  the  Dichsete  and  in  the  not-Dichsete  (straight-winged) 
females.  This  means  that  the  wing-character  Dichsete  does  not 
modify  the  Notch  character  when  present  with  it.  Consequently  we 
should  not  expect  in  Fi  any  difference  between  Dichsete  and  not- 
Dichsete  Notch  females,  due  to  the  Dichsete  gene. 

Table  8. 


V-16241. 
3-1624. . 
>16241 . 
3-1624.. 
r-1624 .  . 
3-16241. 
K-1624.. 
Vl-1624.. 

Total. 


Not-Dichsete  9 


Notch 

9. 


18  atavistic 

8  not  very  atav. . . . 
6+1  atavistic.  .  .  . 

12  not  very  atav .  .  . 

13  atavistic 

15 +2  not  very  atav 

7  atavistic 

4  atavistic 

83+3 


Nol- 
Notch 

9. 


17 
14 

16 
18 
26 
22 
0 
4 


117 


Dichsete  9 . 


Notch 
9. 


7+1  atavistic.  .  .  . 
4+3  not  very  atav 

3  atavistic 

3+1  atavistic .... 

15+3 

3+4 

3+1 

2+1  not  very  atav 

40+14 


Not- 
Notch 

9. 


13 

12 

15 

8 

21 

25 

6 

6 


106 


Not-Dichsete  d^. 


Eosin 
ruby  cT. 


9 
12 
19 
16 
22 
16 
12 

6 


112 


Eosin 


Ruby 


Dichsete 


9 

13 

11 

2 

6 

0 

10 

2 


53 


SHORT  NOTCH. 

Several  times  in  the  early  history  of  the  Notch  stock,  females 
appeared  with  ^ings  much  shorter  than  those  of  the  atavistic  type 
that  can  be  obtained  at  any  time  by  out-crossing  selected  Notch. 
The  general  character  of  the  short-Notch  wing  may  be  gathered  from 
figure  94,  a.  Not  only  is  the  wing  shorter  and  broader,  but  the  end  is 
more  abruptly  and  fully  squared  off  than  in  the  typical  stock  or  in  the 
atavistic  Notch,  figure  94,  b. 

Many  of  the  females  are  sterile,  so  that  the  stock  has  nearly  died 
out  several  times  when  pairs  were  used,  but  mass-cultures  of  this  type 
can  be  kept  going.  Several  times,  when  even  shorter  winged  indi- 
viduals have  appeared,  and  I  have  attempted  to  breed  from  them,  I 
have  found  that  they  were  sterile.  The  stock  was  first  red-eyed,  but 
later  eosin  eye  was  introduced,  so  that  the  X  chromosome  bearing 


GENES   MODIFYING    NOTCH. 


iiO.J 


Notch  has  as  its  mate  in  the  female  an  X  chrom^jsome  l)e^irinK  oosin. 
Such  a  female  crossed  to  an  eosin  brother  gives  1  red -eyed  Notch  9  :  I 


Fig.  94. 

eosin  9  :  1  eosin  cf ,  and  the  expected  number  of  cross-overs.  The 
stock  was  kept  running  by  breeding  in  every  generation  a  number  of 
short-Notch  females  to  some  of  their  eosin  brothers,  the  eosin  sisters 
being  rejected.  No  special  effort  was  made  to  pick  out  the  shortest 
of  the  Notch  females.  The  general  run  of  the  stock  may  be  gathered 
from  table  9  for  the  fourth,  fifth,  and  sixth  generations.     For  some  time 


Table  9.— Short  Notch. 

Notch 

Eosin 

Eo.sin 

Wild- 

Notch 

Eotiin 

E>)sin 

WUd- 

9. 

9. 

d". 

type  cf . 

9. 

9. 

c^. 

ty|)e  cT. 

F4... 

30 

48 

46 

¥,... 

30 

41 

29 

F«... 

20 

10 

18 

5 

¥,... 

47 

57 

41 

¥,... 

24 

13 

13 

Fs... 

39 

30 

58 

¥,... 

29 

41 

36 

F6... 

43 

32 

30 

1 

¥,... 

23 

22 

30 

¥,... 

52 

02 

01 

¥,... 

21 

26 

22 

1 

¥e... 

54 

54 

59 

1 

Ffi... 

84 

71 

78 

F.... 

29 

27 

31 

¥,... 

4 

27 

24 

1 

F,... 

18 

24 

30 

I 

¥,... 

35 

25 

28 

1 

¥,... 

63 

53 

70 

¥i... 

30 

53 

34 



F«... 

80 

55 

00 

I  thought  that  short  Notch  might  be  an  allelomorph  of  Notch — a 
difficult  point  to  settle  if  it  were,  because  there  are  no  males  of  either 
class  to  bring  the  two  allelomorphs  together,  and  no  other  way  of  getting 
them  into  the  same  individual.  But  if  the  shortness  of  this  tyix*  is  due 
to  a  modifying  gene  it  should  be  carried  by  the  not-Notch  males  a.^  well 
as  by  the  female,  and  its  presence  could  be  demonstrated  by  crossing. 


366  GENES   MODIFYING    NOTCH. 

When  a  short  Notch  female  is  out-crossed  to  a  wild  male,  the  daughters 
are  atavistic  (fig.  94,  b) ,  which  proves  that  short  Notch  is  not  due  directly 
to  a  dominant  Notch  unless  the  wild  male  brings  in  a  dominant  gene 
modifying  such  a  dominant  gene.  If  it  does,  then  the  next  F2  genera- 
tion should  give  3  short  to  1  atavistic.  On  the  other  hand,  if  short 
Notch  is  due  to  a  recessive  modifier,  the  F2  ratio  should  be  the  reverse, 
namely,  3  atavistic  to  1  short.  It  may  be  stated  here  that  the  evidence 
shows  that  a  recessive  modifier  is  present,  but  present  in  the  sex- 
chromosome  itself,  so  that  the  numerical  results  follow  the  expectation 
for  sex-linked  inheritance.  The  following  tests  were  made  to  discover 
the  location  of  the  modifying  factor  for  short  Notch : 

FIRST  TEST. 

(1)  A  short  Notch  female  was  crossed  to  a  Star  Dichsete  male. 
The  Star  Dichaete  sons  of  this  cross  get  their  X  chromosome  from 
their  mother,  as  well  as  one  normal  autosome  carrying  the  normal 
allelomorph  of  Star  and  another  that  of  Dichsete.  The  fourth  chromo- 
some pair  may  be  left  out  of  account.  \Mien  such  a  son  is  back-crossed 
to  a  short  Notch  stock  female,  every  Notch  daughter  will  have  one  X 
from  her  mother  and  one  from  her  father  (which  in  turn  came  from  his 
mother,  hence  from  the  short  Notch  stock).  In  other  words,  all  Notch 
daughters  have  the  same  X  chromosomes  as  the  short  Notch  stock 
females.  But  some  of  the  Notch  daughters  will  have  one  Star-bearing 
second  chromosome  and  one  normal  second  chromosome;  others  both 
normal  of  stock.  If  a  recessive  factor  for  short  Notch  was  in  the  second 
chromosome,  the  latter,  containing  both  such  chromosomes,  should  give 
a  shorter  wing  than  the  former.  Similarly  for  Dichsete.  Some  of  the 
Notch  daughters  will  have  a  Dichsete  and  a  normal  third  chromosome, 
others  both  normal  chromosomes  of  the  short  stock.  If  the  modifier 
(shortener)  is  in  the  third  chromosome  the  latter  (both  chromosomes 
present)  should  be  shorter  than  the  former,  etc.  The  results  are  given 
in  table  10. 

This  table  shows  (1)  that  the  short  Notch  reappears  in  this  second 
generation  (back-cross);  (2)  that  it  is  not  more  common  in  the  not- 
Star  than  in  the  Star,  which  means  that  the  modifier  is  not  present  in 
the  second  chromosome;  (3)  that  it  is  not  more  common  in  the  not- 
Dichsete  than  in  the  Dichaete,  which  means  that  the  modifier  is  not  in 
the  third  chromosome;  (4)  it  follows  that  it  must  be  present  either  in 
the  first  or  the  fourth.  The  second  test  (below)  will  show  that  there 
is  in  fact  an  important  modifier  in  the  X  chromosome  itself.  Whether 
another  is  present  in  the  fourth  chromosome  will  be  examined  later 
when  the  atavistic  Notch  flies  that  also  occur  in  table  10  will  be 
discussed. 


GENES    MODIFYING    NOTCH. 


36^ 


It  will  be  noticed  in  table  10  that  in  addition  to  the  nliort  Notch 
there  are  others  called  intermediate  and  even  atavistic.  Tliat  these 
are  for  the  most  part  due  to  fluctuations  of  the  short-Notch  character 
itself  is  almost  certain,  since  even  in  stocks  bred  for  20  nf'tu-'rations 
for  short  Notch  a  similar  range  occurs  in  some  bottles,  but  when  t<'st<'<i 
the  ''atavistic"  (or  more  generally  the  "interniediiitc"  Notch)  Rive 
the  same  kinds  of  daughters  as  do  their  sisters,  the  short  Notch  feniales. 

Table  10. 


Bot. 
No. 

Notch  females. 

Not-Notch  fcmalea. 

2 

Not-Star. 

Star. 

Not-Star. 

Star. 

Not-Dich. 

Dich. 

Not-Dich. 

Dich. 

Not- 
Dich. 

Dich. 

Not- 
Dirh. 

Dich. 

Not  w«. 

Not  w«. 

Nivt  w«. 

Not  w< 

Not 

w«. 

Not 

w*. 

Not 

w«. 

Not 

w«. 

CE. 

CA. 
CA. 

7  short. .  .  . 
1  ^ho^t 

13  short 

2  atavistic. 

4  short .... 

9  short 

6  intcrmed. . 
2  atavistic . . 

10  short 

6  atavistic. 

1  short .... 

1 

24 

5 

6 
14 

3 

.... 

20 
3 

.... 

1 

1 

8 

4 

3 

15 

49 

4 

6 
20 

4 

2  short 

1  short .... 

5  atav.  or 
short. 

3  short 

4  atavistic. . 

1  (?) 

1 

ex. 
ex. 

3  short 

2  atavistic. 

3  atavistic. 

2  atav.  or 
short. 

1 



12 
6 

SECOND  TEST. 

In  this  test  the  reciprocal  cross  was  first  made,  viz.  Star  Dichirte 
female  by  eosin  male  of  short-Notch  stock.  The  Fi  male  gets  his  X 
chromosome  from  his  Star  Dicha?te  mother.  Consecjuently  if  it  is 
the  X  chromosome  in  the  short-Notch  stock  tliiit  carries  a  recessive 
modifier  for  Notch  (that  has  both  the  Notch-bearing  X  and  its  nonmU 
homologous  chromosome)  no  short-Notch  daughters  are  exjx^cted  when 
the  above  Fi  male  is  mated  to  a  short-Notch  stock  female. 

The  result  of  mating  such  Fi  Star  Dicha?te  males  to  short-Notch 
females  is  shown  in  table  11.  Practically  all  of  ttie  Notch  females  are 
atavistic  or  slight  Notch.  The  result  is  in  striking  contrast  to  the 
result  in  the  first  test  and  means,  o))vi()usly,  that  the  X  chromosome 
contains  one  or  more  modifiers  that  shortens  the  ctTects  of  the  Notch 
factor  itself.  That  some  of  the  Notch  fenuiles  are  atavistic  and  some 
slight  may  be  expected,  since  separation  of  the  two  classes  is  difficult 
or  impossible  and  no  emphasis  can  be  laid  on  the  classification  as  it 
stands. 


368 


GENES    MODIFYING    NOTCH. 


THIRD  TEST. 


In  the  second  generation  of  the  first  test  there  were  some  eosin 
Star  Dichsete  males  whose  X  chromosome  should  be  the  same  as  that 
of  the  Fi  males.  Since  the  second  and  third  chromosomes  appeared 
not  to  affect  the  result  in  the  first  test  it  should  not  be  expected  to 
affect  the  result  here,  whichever  ones  are  present.  Half  of  the  sperm  of 
the  males,  however,  should  carry  one  of  the  fourth  chromosomes  of  the 
short-Notch  mother;  the  other  fourth  chromosome  would  be  in  half 
of  the  flies  derived  from  the  same  source  and  in  half  from  the  Star- 


Table  11. 

i 

Bot. 

No. 

Not-Notch  females. 

Notch  females. 

Males. 

Not-Star. 

Star. 

Not-Star. 

Star. 

Not- 
Dich. 

Dich. 

Not- 
Dich. 

Dich. 

Not-Dich. 

Dich. 

Not-Dich. 

Dich. 

Not 
E. 

Eo- 
sin. 

Not 
E. 

Eo- 
sin. 

Not 
E. 

Eo- 
sin. 

Not 
E. 

Eo- 
sin. 

Not  Eosin. 

Not  Eosin. 

Not  Eosin. 

Not  Eosin. 

OA. 
CQ. 

ZZ.. 
GP. 
HK. 

BO. 
BO. 

29 
14 

20 
11 
24 

6 

3 
4 

24 
11 

25 

S 

44 

8 
1 

3 
3 

7 
22 

10 

7 
7 

4  (?) 

6+3  slight.. 

4  atavistic .  . 
2  slight. 

48 
46 

91 

17 

125 

33 

4  atavistic . 
+  1  slight.. 

5  atavistic . 
7  slight...  . 

5  atavistic .  . 
4+1  slight. 
1  short. 

4  atavistic .  . 
9  slight 

or  atavistic 
7  atavistic .  . 

3  atavistic .  . 
6  slight. 

2 

1  intermed. . 

23 

7 

27 
6 

5  atavistic . 

3  atavistic . 
1  atavistic 

or  short. 
2  short 

1  atavistic .  . 

2  slight. 

1  atavistic .  . 
5  atavistic .  . 

3  atavistic .  . 
1    short    or 
atavistic. 

6  atavistic .  . 
3  atavistic .  . 

1  short . 

Dichsete  grandparent.  If  the  fourth  chromosome  causes  the  differ- 
ence between  the  short-Notch  and  the  atavistic  type  it  would  be 
expected  that  some  of  the  males  crossed  to  short-Notch  females  would 
give  one  result  and  some  another  (3:1).  There  were  five  cultures  with 
both  atavistic  and  short  and  one  with  short  Notch  only.  It  is  doubtful 
if  this  should  have  any  significance  (although  it  tallies  wdth  the  expec- 
tation) because  it  is  not  absolutely  certain  that  in  all  of  them  only 
one  male  fertilized  the  female.  The  next  test  was  decisive,  so  that  it 
was  not  necessary  to  repeat  the  experiment. 


GENES   MODIFYING    NOTCH.  300 

FOURTH  TEST  (FOR  FOURTH-CHROMOSOME  MODIFIERS). 

The  following  method  of  findrng  out  whether  a  niodifyinfr  j^cne  it^ 
present  m  a  particular  chromosome  was  su^^ested  by  Dr.  .\.  11.  Sturte- 
vant.  A  short-Notch  female  is  first  crossed  to  a  hhirk  pink  hcnt  nuile. 
The  Fi  males^  are  then  crossed  (in  pairs)  to  stock  short-Notdi  females 
(see  scheme  below). 


Sladk.  pinl^  I-x-tH  6 


W  Slioil  Kotcli  ( 


F„  Notch  p 


b>'  Short  Notch  O 


biy  Black piukb«-nt  O 


Since  the  Fi  male  had  one  fourth  chromosome  from  black  pink  bent 
(and  since  there  is  no  crossing  -over  in  the  male),  half  of  his  Notch  (Fj) 
daughters  will  have  this  chromosome  (only  one  each),  and  half  will  not 
have  it.  If  they  are  of  two  sorts  (so  classified  in  table  12),  such  as 
intermediate  and  short  Notch,  their  differences  might  depend  on  the 
presence  of  the  bent  fourth  chromosome  in  half  of  the  Notch  females. 
If  now  we  separate  as  far  as  possible  the  females  into  two  classes,  and 

Table  12. — Fi  cf  {out  of  short  Notch  9  by  hmt  cf )  by  short  Notch  9  . 


Normal 
9. 

Short 
Notch   ?. 

Interm. 
Notch   9. 

Eosin 
9. 

Eosin 

Eo.«in- 
Notch   9. 

Nonual 

1 

9 

2 

15 
66 
21 

/       22 

I       12 
4 

13 
12 

27 

68 

41 

28 

30 

28 
.30  (2  al- 
most ata- 
vistic). 
6 

36 

15 

73 
122 
47 
60 
32 
40 

14 
51 

/     29 
I     24 

85 
102 
30 
64 
30 
27 

33 
52 
41 

1  (intcrni.) 

•) 

3 

4 

5 

1  (sJiort) 

6 

7.  . 

8 

test  each  female  separately  to  find  out  if  she  has  or  hiis  not  a  l)ent 
fourth  chromosome,  we  should  get  an  answer  to  our  question.  Each 
female  was  bred  to  a  black  pink  bent  stock  male.  The  presence  of 
black,  of  pink,  and  of  bent  (separate  or  combined)  in  the  offspring  wiis 
recorded.  Table  13  gives  the  end-results;  the  first  column  records  the 
kind  of  F2  female  tested,  the  next  three  columns  the  kind  of  notch,  and 
the  next  three  columns  indicate  (by  X)  whether  l)lack.  pink,  or  l>ent 
was  present;  and  the  last  column  the  total  number  of  fliei>. 

*  Their  sisters  that  were  not  recorded  here  wore  nil  atavi.stic  Notch. 


370 


GENES   MODIFYING   NOTCH. 


Inspection  of  table  13  shows  no  significant  correlation  between  the 
kind  of  Notch  shown  by  the  F2  mother  and  the  presence  in  it  of  the 
bent  chromosome  derived  from  the  black  pink  bent  stock;  for  six  F2 
short  Notch  females  had  this  bent  chromosome,  four  did  not;  six  F2 
intermediates  did  not  have  it  and  two  F2  did  have  it.  There  is  no 
correlation  with  black  or  pink  either,  hence  there  were  no  dominant 
autosomnal  modifiers  in  black  pink  bent  stock. 

Table  13. — F2  Notch   9   by  black  pink  bent  cf. 


No. 

Kind  of  F2  9  . 

Notch. 

Bent. 

Pink 

Black. 

Total 
c?  9. 

Short. 

Intermediate. 

Atavistic. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

1.3 

14 

15 

16 

17 

18 

19 

Short     

6 

5 

2 

3 

15 

3 

14 

10 

5 

12 

9 

2 

4 

11 

11 

18 

7 

23 

2 

4 
2 
1 
1 
0 
4 
0 
1 
1 
1 
5 
3 
19 
2 

6 

2 

6 

13 

10 

X 

0 

X 

0 

X 

X 

X 

X 

0 

0 

0 

0 

X 

0 

0 

0 

X 

0 

0 

X 
X 
0 
0 
0 
0 
X 
X 
0 
0 
X 
0 
0 
0 
0 
X 
0 
X 
X 

0 

0 

X 

X 

0 

X 

0 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

X 

0 

33 
20 
33 
12 
76 
15 
47 
20 
17 
50 
33 
3 
75 
49 
53 
40 
59 
97 
21 

Do 

Do 

Do 

Do 

Do 

Do 

Do 

Do 

Do 

Do 

Intermediate . . 

Do 

Do 

Do 

Do 

Do 

Ata\astic 

Do.  (almost). 

RECOMBINATION  OF  BENT  AND  SHORT  NOTCH. 

As  a  matter  of  cm-iosity,  largely,  the  possible  interaction  of  ''bent" 
in  double  dose  on  Notch  was  determined.  Flies  of  the  desired  recom- 
bination were  made  by  crossing  bent  males  to  short-Notch  females  and 
then  by  breeding  the  Fi  Notch  females  to  their  brothers.  Amongst  the 
F2  flies  were  pure  bent  females  that  were  also  Notch.  These  showed 
the  wddest  possible  range  of  modification  as  does  the  bent  character 
itself.  In  extreme  cases,  as  shown  in  figure  95,  the  wing  is  as  narrow  as 
stumpy  wings  (see  Critique  of  Theory  of  Evolution,  p.  11,  figure  5, 
c,  d).  It  is  noticeable,  too,  when  looking  through  such  a  series,  that 
the  extent  to  which  the  bent  factor  manifests  itself  in  other  ways,  such 
as  in  the  shortening  of  the  legs,  is  a  sort  of  index  of  the  extent  to  which 
the  wing  is  affected.  This  might,  on  first  thought,  be  interpreted  as 
furnishing  evidence  in  favor  of  the  view  that  the  extent  to  which  a 
character  develops  may  be  an  index  of  the  quantity  of  the  gene  present 


GENES   MODIFYING    NOTCH. 


371 


in  the  egg.  But  since  bent  flies  with  the  clmnict^r  well  develoi>ed  nmy 
not  produce,  when  bred  to  each  other,  any  more  flies  of  their  own  kind 
than  do  their  normal  appearing  brothers  and  sisters,  there  is  nothinK 
gained  by  making  such  an  assumption.  On  the  contrary,  it  8eem« 
more  reasonable,  I  think,  to  suppose  that  the  siime  environment  (in 
the  widest  sense)  that  is  favorable  to  the  full  development  of  tiie  bent 
characters  make  that  character  the  more  effective  in  its  influence  on 
short  Notch.  It  seems  to  me  hazardous  to  base  any  view  concerning 
the  nature  of  the  gene  itself  on  evidence  of  this  kind,  as  lias  Imvu  done 
by  several  recent  writers. 


FiQ.  95. 


CROSSES  BETWEEN  SHORT  NOTCH  AND  OTHER  STOCKS. 

Unless  the  modifying  factor  for  short-Notch  is  partially  dominant  or 
unless  other  stocks  carry  the  modifier,  or  some  other  dominant  modi- 
fier, the  expectation  on  crossing  short-Notch  females  to  males  of  other 
stocks  is  atavistic  types  of  Notch  females.  The  males  of  short-Notch 
stock  carry  in  their  sex  chromosome,  as  has  been  shown,  a  modifier  for 
short-Notch;  hence  crossing  of  such  males  to  selected  or  to  atavistic 
Notch  are  expected  to  show  some  influence  on  the  character  of  Notch 
in  their  daughters  if  the  factor  is  dominant  or  partly  so.  In  the  light 
of  these  expectations  the  following  crosses  are  not  without  interest. 


372 


GENES  MODIFYING  NOTCH. 


SHORT  NOTCH  BY  STAR  DICHy^TE. 

There  were  four  crosses  of  this  combination  that  gave  in  Fi  Notch 
females  with  intermediate  wings  shorter,  on  the  average,  than  the 
atavistic  type,  and  therefore  more  on  the  order  of  the  short  type. 
The  Fi  records  are  as  follows : 


Notch- 
Dichsete  9  • 

Notch 
9. 

Normal 
9. 

Normal 

a". 

Dichsete 

Dichsete 

9. 

11 

17 
6 

24 
2 

11 

8 

17 

4 

S 

9 

14 

3 

11 
9 
4 

9 
5 

7 

8 
15 

In  these  results  the  condition  of  the  wings  was  the  same  in  the 
Dichsete  female  and  in  those  not-Dichsete,  showing  that  the  gene  of 
the  latter  does  not  itself  act  as  a  modifier.  This  information  is  of 
value  in  working  out  the  location  of  the  modifier  by  means  of  the  S'  D' 
test.  The  further  fact  that  the  Fi  females  were  ''intermediate"  be- 
tween atavistic  and  short-Notch  is,  then,  more  probably  due  to  some 
other  modifier  of  the  Star  Dichsete  short  Notch.  This  compHcation 
makes  it  more  difficult  to  interpret  the  results  when  Star  Dichsete  is 
used  to  locate  the  modifier  of  short  Notch,  but  still  leaves  such  a  test 
possible,  as  the  following  experiments  show. 


SHORT  NOTCH  BY  EOSIN  RUBY  FORKED. 

When  short-Notch  females  were  crossed  to  eosin  ruby  forked  males 
of  stock  the  Fi  Notch  females  had  in  nearly  all  cases  shorter  wings  than 
the  atavistic  notch  flies  (or  ordinary  Notch)  obtained  in  other  cases 
(four  are  drawn  in  fig.  96,  a,  b,  c,  d).  In  these  instances  the  eosin 
ruby  forked  males  may  carry  not  only  the  normal  allelomorph  of  the 
selected  modifier,  but  also  another  gene  that  carries  the  Notch  towards 
the  short-Notch  direction,  which  might  be  the  modifier  in  the  X 
chromosome  of  the  father.  The  F2  generation  came  from  the  short- 
like Notch  Fi  female  by  her  brother.     The  records  are  as  follows: 


Notch. 

Normal. 

1 

2 

3 

33  intermediate  short. . . 
90  atavistic 

56 

108 

76 

91  short   

The  failure  to  sharply  distinguish  between  the  types  of  Notch  in 
these  F2  counts  shows  that  without  first  purifying  the  eosin  ruby 


GENES    MODIFYING    NOTCH. 


373 


forked  stock,  that  stock  is  not  suited  to  t^st  the  location  of  the  reRular 
modifier  for  short  Notch.     The  experiment  was  not  carried  further. 

Reciprocally,  when  the  male  of  short-Notch  stock  was  crossed  to 
selected  female,  the  Fi  Notch  females  were  atavistic,  indiratiiiK  thiit 
the  Notch  gene  of  the  selected  stock  lias  not  itself  clianged,  and  that 


Fia.  96. 


374 


GENES   MODIFYING   NOTCH. 


the  short  type  carries  the  normal  allelomorph  of  the  selected  modifier. 
(Fig.  97,  a,  h,  c,  d.)     The  Fi  counts  gave: 


Notch 
(atavistic). 

Normal  9  • 

Normal  cf. 

17 

18 
17 
13 
33 
14 
22 

9 
20 

5 
38 
11 

7 

19 

8 

24 

15 

16...; 

The  reciprocal  cross  was  also  made,  viz,  short  Notch  female  by 
male  of  selected  stock,  with  results  in  Fi  as  follows: 


Notch 
(atavistic). 

Normal  9  • 

Normal  cf. 

13    

28 
9 

28 

19 
18 
29 

13 

23 

It  is  evident  from  the  first  cross  that  the  gene  for  short  Notch  in  the 
sex  chromosome  of  the  male  does  not  carry  a  dominant  allelomorph 
for  short  Notch,  and  not  even  one  that  when  heterozygous  makes  the 
Notch  any  shorter  than  in  the  atavistic  flies.  It  is  evident  from  the 
second  reciprocal  cross  that  the  modifying  gene  for  short  Notch  carried 
by  the  other  sex  chromosome,  viz,  the  one  that  carries  Notch  also,  is 
likewise  not  a  dominant  or  even  a  modifier  when  in  heterozygotic 
condition.  Both  crosses  show  that  the  selected  stock  is  free  from 
modifiers  for  making  Notch  shorter  than  the  atavistic  Notch. 

In  four  cases  the  cross  between  short  Notch  and  black  pink  bent 
was  carried  to  the  F2  generation  (instead  of  back-crossing  as  above) 
with  the  following  results: 


Notch. 

Total 
all  flies. 

Short. 

Intermediate. 

10 

21 

74 

3 
0 

1 

59 

94 

143 

In  this  case  the  Fi  male  gets  his  single  X  chromosome  from  his 
mother,  viz,  an  X  with  the  shortening  factor.  His  sisters  have  one 
Notch  X  chromosome  carrying  the  shortener  and  another  from  the 
bent  father  without  the  shortening  factor.  Hence  the  expectation  in 
F2  is  that  all  the  Notch  flies  should  be  short-Notch  except  for  crossover 
cases,  where  the  gene  for  short-Notch  carried  into  the  X  is  derived  from 


GENES   MODIFYING   NOTCH. 


375 


the  bent  father.  The  results  agree  with  the  expectation.  The  few 
intermediate-Notch  flies  may  be  such  crossovers  or  more  probably 
fluctuations  of  the  short  type. 


Fig.  97. 


376 


GENES   MODIFYING   NOTCH. 


CLASSIFICATION  OF  TYPES  OF  NOTCH. 

In  the  preceding  crosses  between  short  Notch  and  other  races,  I  was 
handicapped  by  the  difficulty  of  giving  a  more  exact  classification  of 
the  types  called  atavistic,  intermediate,  and  "short"  Notch.  In  order 
to  get  a  more  objective  classification  three  characteristic  flies  were 
picked  out  from  the  short-Notch  stock  (that  had  been  inbred  for  at 
least  25  generations,  although  not  in  pairs),  and  drawn  (fig.  98,  a,  h,  c). 


Fig.  98. 

The  left-hand  figure,  a,  corresponds  to  the  type  called  intermediate  in 
hybrid  Notch  flies;  the  second,  b,  is  a  common  type  somewhat  shorter 
than  the  last  and  in  crosses  would  ordinarily  be  placed  with  the  next 
type,  c.  This  type  is  the  predominating  type  in  "good"  short-Notch 
stock. 

In  contrast  to  type  a,  the  type  called  atavistic  is  shown  in  figure  94,  h. 
These  two  types  overlap,  but  in  a  given  case  one  or  the  other  type  is 
found  in  the  great  majority  of  individuals. 


GENES   MODIFYING    NOTCH. 


A  census  of  the  short-Notch  stock  taken  at  the  wimo  time  that  the 
two  following  records  were  m;ide  (April  1918),  and  iind«;r  tijc  s;iin<'  con- 
ditions, gives  for  these  ma^s-cultures  the  results  shown  in  table  14. 

Table  U.— Short-Notch  stock  for  control.    {Sh.  Notch   9   by  eottin  cf  •) 


Bottle. 

Eosin  cf . 

Eosin  9. 

Normal  9  • 

Atttvialic. 

a. 

a+. 

b. 

6+. 

c. 

1 

20 
16 
96 

29 

13 

110 

3 

3 

1 
14 

13 
10 
41 

2 

3 

1 
3 

1 

3 

7 

10 

Total 

132 

152 

4 

1 

3 

7 

13 

18 

M 

Here,  as  is  usual,  an  eosin-eyed  father  had  been  bred  to  a  red-eye<i 
short-Notch  mother.  The  expected  classes  (non-crossovers  and  cross- 
overs) are  given  in  the  first  three  columns,  while  the  red-eyed  Notch 
females  are  put  into  five  classes  that  follow,  viz,  type  atavistic;  type 
a,  "intermediate";  type  «-|-  "intermediate"  standing  between  a  and 
b;  type  b  "common"  short  Notch;  type  6+  standing  between  b  and 
c;  and  type  c  "short  Notch,"  the  modal  class. 

A  cross  between  sisters  of  the  mothers  of  the  above  stock  (short 
Notch)  and  wild  males  was  made.  The  Fi  results  are  shown  in  table 
15,  in  which  the  same  classification  of  the  Fi  Notch  females  as  that 
just  given  for  the  stock  control  was  made. 


Table 

15— Short    Notch    9 

by  mi 

Id  & 

Bottle. 

Normal 
9. 

Normal 

Eosin 

Ata- 
vistic. 

At. 
1    wiiiR. 

a. 

a+. 

b. 

6+. 

e. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

Total . 

10 
9 
42 
13 
23 
3 
48 
34 
23 
47 
18 
5 
17 
26 
37 

2 

4 
47 
18 
18 

5 
30 
30 
12 
4S 
14 

9 
21 
22 
11 

7 

1 

32 

1 

3 
4 

1 

2 
5 
5 
11 
8 
3 

1 
1 
1 
1 
1 
2 

4 
o 

3 
2 

4 
3 
5 
2 

4 

2 

4 

6 
3 
1 
2 

4 

1 
1 

5 

1 

7 

1 

23 
20 

3 
29 

1 

1 

1 

3 
5 
3 

1 
4 
1 

2 
2 

1 
3 

1 
•> 

3 

18 
20 

3 
1 
4 

2 

355 

6 

291 

164 

7 

40 

32 

33 

14 

8 

Table  15  shows  the  wide  variability  of  Fi.  The  extreme  plus  variant,*^. 
i.  e.,  the  extreme  short  Notch  class,  are  owing  to  three  bottle-s  where 
non-virginity  of  the  female  would  be  the  sinii)lest  solution  were  it  not 
that  only  12-hour  females  were  used,  which,  wliile  still  leaving  open 


378 


GENES   MODIFYING   NOTCH. 


some  question  as  to  the  virginity  of  the  mother,  yet  makes  that  inter- 
pretation unHkely.  It  seems  to  me  more  probable  that  in  these  three 
cases  the  father  carried  a  modifier  for  Notch.  Excluding,  likewise 
No.  9  on  the  same  grounds,  it  is  evident  from  this  table  that  the  ata- 
vistic types  predominate. 


Fio.  99. 


As  I  stated  the  yellow  prune  forked  stock  crossed  to  short  Notch  had 
given  in  Fi  so  many  intermediate  flies  that  the  experiment  undertaken, 
to  locate  the  short-Notch  factor  in  the  sex  chromosome  had  to  be 
abandoned.     A  year  later  the  forked  flies  had  disappeared  from  this 


GENES    MODIB^YING    NOTCH. 


379 


stock,  so  that  only  yellow  prune  flies  ct)uki  Ik»  utilized  to  again  t««t  thiB 
cross.     The  results  confirmed  the  earlier  ones,  as  seen  in  table  10. 

The  flies  in  all  but  one  culture  (No.  4)  j^ive  nearly  the  saine  re«ult« 
as  do  the  short  Notch  short  females  l)red  to  their  own  Ht<K-k  males. 
Either  the  same  factor  for  short  Notch  is  carried  by  yellow  prune  that 
is  present  in  the  short  Notch  stock,  or  else  some  other  factor  tluit  Iuih 
a  closely  similar  effect.  As  yet  I  have  not  put  this  (juostion  to  a  U^i. 
Culture  No.  4  gave  such  a  different  result  from  the  other  five  that  it 
is  almost  certain  that  the  "short"  modifier  was  absent  in  thi.s  ca^se. 

Table  16. — Short  Notch    9    by  yellow  prune  cf. 


Bottle. 

Normal 

9. 

Normal 

Eo3in 

Eosiii 

9. 

Yellow- 
prune  d^. 

Ata- 
vistic. 

At. 
1  wing. 

A. 

A-J-. 

B. 

B-I-. 

C. 

1 

2 

3 

4 

5 

6 

Total . . 

15 
33 
1 
114 
24 
23 

2 



22 

41 

2 

109 

28 
16 

3 

3 

4 
6 

5 
10 

1 

27 

8 

7 

7 
11 

2 
11 
16 
18 

4 

3 

7 

4 

26 

1 

3 

32 
3 

3 

1 

210 

2 

218 

3 

11 

4 

31 

6 

47 

68 

65 

ABERRANT  NOTCH  WINGS. 

In  the  course  of  the  selection  experiment  a  few  individuals  appeared 
in  which  the  wings  showed  an  extreme  condition  of  Notch.  Tliat 
these  rare  cases  were  due  to  some  abnormal  condition  that  influenced 
the  development  of  the  wing  is  shown  by  the  fact  that  in  most  cases 
only  one  wing  was  affected,  as  shown  in  the  three  cases  drawn  in  figure 
99,  a,  b,  c,  and  by  the  fact  that  when  these  were  bred  the  offspring  were 
of  the  usual  Notch  type.  When  both  wings  were  affected  (fig.  90.  a) 
the  flies  were  usually  sterile.  Possibly  the  results  were  due  to  soniiitic 
mutation,  but  this  is  not  very  probable.  Two  of  the  three  flies  had 
one  normal  wing,  but  the  eye-color  showed  that  the  flies  were  gene- 
tically Notch.  Similar  modifications  were  seen  in  the  eosin  ruby 
sisters  of  these  flies  that  did  not  contain  the  Notch-bearing  gene. 

DEFORMED  EYES. 

From  time  to  time  flies  appear  in  the  Notch  stock  in  which  one  or 
both  eyes  are  reduced  (fig.  100),  sometimes  to  mere  specks.  .Ml 
attempts  to  breed  such  a  type  have  been  futile  (although  the  males 
at  least  are  fertile)  and  all  attempts  to  cause  them  to  apix^ar  in  larger 
numbers  by  alterations  in  the  environment  (heat,  cold,  acidity,  mois- 
ture) have  failed.  The  remnant  of  the  eye  arouses  a  suspicion  t  hat  t  he 
eye  has  been  injured  either  by  the  larvae  in  feeding  or  el.se  by  shaking 
the  bottle  containing  the  pupae.     We  meet,  not  rarely  in  other  st«M-ks, 


380 


GENES    MODIFYING    NOTCH. 


with  injured  eyes  that  have  developed  into  smaller  eyes,  i.  e.,  dwarf 
whole  eyes.  Three  conditions  make  this  interpretation  improbable. 
In  the  first  place,  the  reduced  eyes  are  often  identically  the  same  on 
the  two  sides,  which  would 
scarcely  be  expected  if  due 
to  accidental  puncture  by  a 
larva.  In  the  second  place, 
several  individuals  with  re- 
duced eyes  often  appear 
at  the  same  time,  while  for 
long  periods  none  at  all  are 
present.  Some  unknown 
environmental  factor  would 
seem  the  most  probable  ex- 
planation, especially  when 
the  offspring  of  Notch  in- 
dividuals do  not  repeat  the 
eye  condition.  Probably 
some  lethal  combination 
may  be  involved.  In  the 
third  place,  the  individuals 
which  are  not  Notch  have 
never  shown  this  modification  of  the  eyes.  At  the  time  when  the  de- 
formed eye  was  most  frequent  (winter  of  1917)  records  were  kept  of 
its  frequency  in  mass-cultures  (usually  F2  parents  and  F2  offspring). 


Fig.  100. 


Gen. 

Notch. 

Deformed. 

Red  notch 

9. 

Red  deformed 

9. 

Eosin 
9. 

Eosin 

F3 

F3 

F— 

F4 

1913 

2475 

36980 

18 
20 
10 

12 
72 
26 
20 
14 
24 
19 
30 
22 

1 
10 
13 

65 

78 
85 
38 
79 
18 
74 
29 
37 

70 
83 
52 
27 
71 
25 
59 
33 
31 

Fs 

Fi 

Ft :.. 

Fe 

F7 

""'t'" 

2 
0 

F7 

F7 

Ft 

In  the  culture  F5  there  were  13  Notch  with  deformed  eyes.  These 
were  all  bred  together  with  their  normal  brothers  and  sisters  with 
eosin  eyes  and  gave : 

Fe:  Notch  9  ,  56;  deformed  9,4;  eosin  9  ,  65;  eosin  cJ',  48. 

The  offspring  of  this  line,  part  of  which  are  included  in  the  F7  count 
in  the  preceding  table,  gave  occasionally  deformed-eyed  flies,  but  not 
more  frequently  than  sister  cultures. 


PLATE  1? 


t 


GENES   MODIFYING    NOTCH. 


381 


LITTLE  EYES. 

There  appeared  in  the  SS  AAA  334G2G2  pcnoration  of  tho  Rolcrtod 
stock  some  mutant  flies  that  had  not  only  the  wings  sonicthinK  like 
thoseof  Notch, but  theeyewasalsoof  tenreduced  (plate  \2,a,b,c).  Since 
the  latter  condition  had  been  also  found  occiusjoiuilly  in  short  Htock, 
the  occurrence  here  of  this  new  type,  called  little  eyes,  sugKosted  the 
possibility  that  a  new  allelomorph  of  Notch  \\iid  appe^ired.  Tim  fwjuel 
shows  the  futility  of  any  such  judgment  in  regard  to  the  gene  hm^l 
on  the  appearance  of  the  character.  The  now  mutant  proved  to  Iki  so 
weak,  so  inviable,  and  so  infertile  that  almost  nothing  could  l>e  done 
with  it.  It  could,  in  fact,  only  be  kept  in  exist^jncc  by  large  mass- 
cultures  of  flies  known  to  contain  the  genes.  The  females  never  bred, 
although  many  attempts  were  made  to  breed  them.  A  few  males 
mated  to  ruby  females  gave  offspring,  and  these  F,  flies  gave,  along 
with  many  normal  offspring,  a  few  small-eyed  flies  of  both  sexes.  The 
numbers  were  very  small,  but  as  both  males  and  females  were  present, 
the  result  shows  that  the  character  is  not  sex-linked  and  therefore 
that  it  can  not  be  an  allelomorph  of  Notch.  The  location  of  the  gene 
in  its  chromosome  was  not  made  out  because  the  stock  died.  It 
will  be  noted  that  two  of  the  females  figured  have  x  m 
Notch-like  wings,  while  the  other  female  and  the  male 
have  rounded  wings.  It  is  probable  that  the  two 
females  really  had  the  Notch  gene,  since  the  mutant 
arose  in  the  stock,  but  other  females  were  not  Notch,  as 
shown  here  and  as  frequently  observed  in  later  cultures. 
There  is  no  evidence  that  any  males  were  notched, 
although  the  beading  might  closely  resemble  notching. 
Great  variability  of  the  character  was  observed— in 
fact,  some  individuals  could  be  detected  only  by  the 
very  shghtly  smaller  eye  or  a  tendency  for  the  wings 
to  spread  out. 

HIGH  SEX-RATIOS  CAUSED  BY  LETHALS. 

Notch  is  a  recessive  lethal,  and  if  by  chance  another 
lethal  had  been  present  in  the  X  chromosome  from  the 
father  of  such  a  female,  all  of  her  sons  would  die  except 
the  occasional  son  due  to  crossing-over  between  the 
lethal  factors.  For  instance,  if  the  Notch  gene  has 
the  location  shown  in  figure  101  and  another  lethal 
factor  in  the  other  chromosome  located  as  shown  in  the  Fio.  loi. 
same  figure,  then  either  chromosome  tliat  goes  into  an  egg  that  is  later 
fertihzed  by  a  Y-bearing  spermatozoon  will  die,  but  by  crossing-over 
between  the  Notch  and  the  lethal  loci  there  will  he  produced  one  rhr(v 
mosome  bearing  two  lethals,  and  another  with  their  normal  allolo- 


)>«*ck 


Ulhai 


382 


GENES    MODIFYING    NOTCH. 


morphs ;  the  former  will  be  expected  to  kill  any  male  that  gets  it,  the 
latter  should  give  normal  males.  Hence  a  few  males  are  expected 
under  these  circumstances — the  number  depending  on  the  '' distance" 
apart  of  the  lethals  involved.  Two  cases  in  which  lethals  appeared 
are  given  below: 


Notch 

9. 

Normal 

9. 

Eoiin 
ruby  9 . 

Eosin 
ruby  cf . 

Eosin 

Ratio. 

X  667763 .  .  . 
SSO  1122.  .  . 

5+6 
44     4 

36 
71 

29 

1 
9 

1 

76  9   to    1  d". 
119  9  to  10  d". 

The  question  of  origin  of  the  new  lethal  that  appeared  is  not  with- 
out interest.  All  of  the  eggs  must  contain  it  in  the  X  chromosome 
allelomorphic  to  the  one  carrying  Notch;  hence  it  must  have  arisen 
in  a  single  primordial  cell  from  which  all  the  cells  of  the  ovary  have 
come,  or  else  it  must  have  been  present  in  the  single  spermatozoon  that 
fertilized  the  egg  from  which  the  female  in  question  developed.  Since 
the  new  lethal  is  here  contained  in  the  eosin-ruby-bearing  chromosome 
it  is  shown  to  have  come  from  the  male,  and  it  seems  probable  here 
(although  not  ej^licitly  shown  since  the  behavior  of  the  sisters  is  not 
recorded  in  the  table),  from  a  single  one  of  his  spermatozoa,  viz,  the 
one  that  fertilized  the  female  under  discussion.  If  subsequent  work 
proves  that  when  this  kind  of  lethal  arises  the  sisters  of  the  lethal- 
bearing  female  are  not  lethal-bearing,  it  follows  that  the  mutation  took 
place  in  the  last  stages  of  the  formation  of  the  spermatozoon  and  per- 
haps at  the  time  of  maturation  (which  would  give  two  such  sperm),  or 
even  later  after  the  sperm  itself  is  formed. 

The  complete  proof  that  the  high  sex-ratios  here  found  are  due  to  a 
lethal  can  only  be  established  by  breeding  the  daughters  and  by  show- 
ing, as  has  been  done  in  other  such  cases  of  high  sex-ratios,  that  two 
lethals  were  present.  As  this  point  has  been  sufficiently  established 
in  other  instances,  it  was  not  thought  worth  while  to  test  it  out  here. 

OTHER  CHARACTERS  THAT  LOOK  SOMETHING  LIKE  NOTCH. 

In  the  course  of  the  selection  experiment  a  number  of  other  charac- 
ters have  come  up,  and,  since  they  involved  the  ends  of  the  wings,  might 
be  taken  by  a  neophyte  as  modifications  of  Notch  or  even  perhaps  as 
"  caused  "  by  the  selection  of  Notch.  Two  points  may  be  noticed  here : 
first,  that  three  of  these  mutations  at  least  were  in  the  direction 
opposite  to  the  direction  of  selection,  and  second,  that  they  might 
act  as  modifiers  of  the  character  selected,  even  although  they  hap- 
pened to  be  mutations  already  known. 

Cut  is  a  mutant  with  outer  and  inner  edge  of  wing  cut  off,  leaving 
a  pointed  end  (fig.  102).  It  is  a  well-recognized  character  and  appeared 
in  a  male  in  one  of  the  selected  cultures,  viz,  SS  AAA  874626114. 


GENES   MODIFYING    NOTCH. 


383 


Truncate  is  a  mutant  that  frequently  appears  in  our  cultures.  It 
has  also  appeared  in  the  selection  experiments.  The  cnd.s  of  the 
wings  are  cut  off  squarely.  As  it  is  dominant,  esjK'ciiilly  in  certain 
stocks,  it  is  hkely  that  it  would  much  effect  the  character  of  the  Notch 
when  it  occurred  with  it.  Truncate  appeared  several  times  in  the 
course  of  the  experiment. 
The  character  of  the  trun- 
cate Notch  flies  is  shown  in 
figure  103,  a,  b,  c,  d. 

Beaded  has  appeared  sev- 
eral times  in  the  course  of  the 
work  (fig.  104),and  while  no 
tests  have  been  made  to 
establish  its  relation  to  stock 
beaded,  it  is  not  unlikely  that 
it  is  sometimes  the  same. 
Since  beaded  often  affects  the 
ends  of  the  wings,  and  since 
Notch  itself  often  has  a  de- 
fective outer  margin  to  the 
wing,  the  similarity  of  the 
two  stocks  is  in  some  flies  very 
striking.  But  the  common 
beaded  is  not  sex-hnked. 

A  stock  which,  when 
crossed  to  vestigal,  produces  flies  many  of  which  have  a  Notch  on  the 
end  of  the  wings  has  been  isolated  by  Dr.  C.  B.  Bridges.  It  has  no 
relation  to  Notch  and  appears  in  both  sexes.  (See  "Nick, "  page  273, 
Part  II.) 

On  several  occasions  males  (also  females)  have  been  found  in  which 
a  Httle  piece  is  cut  out  from  the  end  of  one  or  from  both  wings,  (fig. 
105  a,  5,  c).  Superficially  one  gets  the  impression  that  the  Notch 
character  has  appeared  in  a  male.  These  males  have  l)een  bred,  and 
have  never  transmitted  the  character,  so  that  there  can  be  no  doubt 
that  the  variation  has  nothing  whatever  to  do  with  Noteh  and  is 
possibly  only  a  somatic  defect,  or  more  probably  is  a  nuiltiple-factor 
character.  The  only  way,  in  fact,  that  Notch  might  appear  in  a  nuile 
would  be  through  somatic  segregation  in  a  female  embryo  of  such  a 
kind  that  the  Notch-bearing  chromosome  became  dislocated  and  car- 
ried to  the  anlage  of  the  wing,  leaving  the  other  chromosome  to  j)ro(luce 
a  male.  Such  a  result  has  not  been  observed  ami  it  would  be  diflicult 
to  establish  the  case  if  it  really  occurred.  The  sex-linked  nuitant 
"serrate"  that  was  present  in  the  Star  Dicha^te  stock  is  also  a  gi>od 
mimic  of  Notch. 


Fiu.  102. 


384 


GENES   MODIFYING   NOTCH. 


GYNANDROMORPH;  NOTCH  EOSIN  RUBY. 


In  generation  SS  11240521114  of  selected  Notch,  an  individual  was 
found  that  was  female,  red-eyed  and  Notch  wing  on  one  side  and 
male,  eosin  ruby-eyed  and  normal  wing  on  the  other  side  of  the  body. 
The  mother  of  this  fly  had  an  X  chromosome  containing  the  gene  for 


Fig.  103. 

Notch  and  the  normal  allelomorphs  of  eosin  and  ruby  (viz,  red),  and 
another  X-chromosome  containing  the  genes  for  eosin  and  ruby  eye- 
colors.  All  of  the  characters  for  which  these  genes  stand  appear  in  this 
individual.  An  egg  containing  the  Notch-bearing  X  must  have  been 
fertihzed  by -a  sperm  containing  the  eosin  ruby  genes.  At  some  time 
in  the  early  history  of  one  of  the  segmentation  di\isions  of  a  nucleus 
of  this  egg,  the  eosin  ruby-bearing  X  chromosome  must  have  divided 
normally,  while  at  the  same  time  one  daughter  chromosome  of  the 


GENES   MODIFYING    NOTCH. 


385 


Other  X  (the  Notch-bearing  chromosome)  must  Imvo  Uikko.!  U-lund  at 
some  division  with  the  result  that  one  cell  g.,t  both  X's  and  the  othe 
cell  only  one  X.  "ii«i-i 

In  consequence  of  such  a  process  of  chromatin  oliminati(,n  we  ex- 
pect one  part  of  the  individual  to  be  male  a.s  well  a«  osin  rubv  and  the 


Fia.  104. 


Fig.  105. 

other  part  female,  red-eyed  and  notched.  An  examiniition  of  Plate 
4,  figure  2  shows  that  the  right  side  is  female,  as  .seen  in  the  wings,  the 
eye,  and  the  foreleg  (absence  of  sex-comb),  and  that  the  left  side 
is  male,  as  seen  in  the  size  of  the  wing,  color  of  eye,  and  sex-comb.  This 
gynandromorph  is  not,  however,  strictly  bilateral,  for  thoupjier  posterior 
corner  of  the  light-colored  eye  is  red,  while  the  tip  of  the  abdomen. 


386  GENES   MODIFYING   NOTCH. 

especially  on  the  right  side,  is  male.  The  genitalia  (not  shown  here) 
are  like  those  of  the  normal  male.  While,  therefore,  there  is  no  such 
sharp  line  of  division  as  is  found  in  many  Drosophila  mosaics  and  gynan- 
dromorphs,  yet  the  distinction  between  the  characters  in  the  different 
regions  is  sharp.  There  is  nothing  in  the  hypothesis  of  chromosomal 
elimination  that  requires  that  the  critical  division  should  occur  so  early 
that  the  nuclei  that  go  to  one  half  of  the  egg  are  separated  from  those 
that  go  to  the  other,  or  that  even  if  it  occurs  at  a  very  early  division  the 
separation  of  the  two  groups  of  nuclei  need  be  exactly  medial. 

The  critical  evidence  obtained  in  other  Drosophila  gynandro- 
morphs  proves  that  abnormality  must  have  been  due  to  chromosomal 
elimination  rather  than  to  other  processes,  such  as  those  suggested 
earlier  by  Boveri  (1883)  and  by  myself  (1905)  to  account  for  other 
gynandromorphs.  The  critical  evidence  rests  on  the  presence  in  the 
two  parents  of  a  pair  of  genes  in  other  than  the  sex  chromosome. 
The  same  analysis  can  not  be  used  in  a  case  of  this  kind  where  only 
sex-linked  characters  are  involved. 

An  examination  of  this  case  from  the  point  of  view  of  the  two 
other  hypotheses  referred  to  above  leads  to  the  following  analysis: 
Boveri's  view  calls  for  belated  fertilization,  so  that  the  entering  sperm 
unites  with  one  only  of  the  two  first-division  products  of  the  egg- 
nucleus.  Now,  in  this  case  we  know  that  the  egg-nucleus  contained 
the  genes  for  red-eyed  and  Notch,  hence  the  products  of  such  a 
division  also  contained  these  genes.  If  then  to  one  of  them  the  sperm- 
nucleus  is  added  (bearing  the  eosin  ruby  genes)  that  half  will  give  rise 
to  female  parts  having  the  dominant  character  (red  eyes  and  Notch 
wings),  and  the  other  first  divisional  product  of  the  nucleus  (haploid 
with  one  X),  while  expected  to  produce  male  parts  perhaps,  yet  such 
male  parts  would  have  red  eyes  and  Notch  wings  also.  Clearly 
Boveri's  view  will  not  fit  this  case. 

On  my  earlier  view,  gynandromorphs  in  insects  may  arise  from  super- 
numerary fertilizations.  In  this  case  we  must  suppose  that  two 
female  producing  sperms  enter  the  egg,  one  fusing  with  the  egg-nucleus 
and  give  rise  to  the  female  parts,  the  other  developing  separately  and 
giving  rise  to  the  male  parts,  which  would  then  have  the  eosin-ruby 
eye-color  and  normal  wings.  My  own  hypothesis  fits  the  present  case, 
but  I  think  nevertheless  that  all  such  cases  in  Drosophila  are  more 
probably  due  to  elimination  because  where  critical  evidence  has  been 
obtained  it  shows  beyond  doubt  that  the  result  was  due  to  chromo- 
somal elimination. 


GENES   MODIFYING    NOTCH.  [^J 

SUMMARY. 

(1)  Mass  selection  on  a  dominant  character  called  Notch  \v:i.s  ,■  irntni 
out  through  24  generations  of  Drosophila  melanoga^icr ,  with  the  rc-sult 
that  a  change  occurred  in  the  du-ection  of  selection.  Notch  win^ 
is  caused  by  a  dominant  gene  in  the  sex-chromosome.  Inadtlition 
to  its  dominance,  the  gene  produces  a  recessive  lethal  efTect,  killing 
every  male  that  carries  the  gene.  Notch  females  are  heterozyKou.s  for 
the  Notch  gene,  i.  e.,  one  X  chromosome  carries  the  gene  for  Notch,  the 
other  X  chromosome  its  normal  allelomorjih.  The  latter  sa\-e«'  the 
female  from  the  letlial  effect  of  the  Notch  gene.  Since  no  Notch  niiilen 
exist,  it  is  not  possible  to  state  whether  the  Notch  gene  would  also  l>e 
lethal  in  double  dose  in  the  female,  but  that  such  is  almost  certainly  the 
case  is  shown  by  the  absence  of  such  females  that  might  arise  throiigli 
equational  nondisjunction,  i.  e.,  by  two  Notch-bearing  chromosomeh 
remaining  in  an  egg  that  was  then  fertilized  by  a  Y  sperm.  Such  a 
female,  if  she  could  be  produced,  would  have  no  sons,  and  all  of  her 
daughters  would  be  Notch  (instead  of  half  of  them  as  usual).  No  such 
female  appeared.  The  case  of  two  females  with  high  sex-ratios  de- 
scribed in  this  paper  are  show^i  to  be  due  to  a  letlial  fact<>r  that  had 
appeared  in  the  ''normal"  X  chromosome  of  the  father  of  the  fcnuile  in 
question,  etc. 

(2)  By  a  suitable  method  described  in  the  text  it  is  shown  that  the 
changes  brought  about  by  selection  were  due  to  the  presence  in  the 
stock  of  a  recessive  modifying  factor  in  the  second  chromosome.  Notch 
females  homozygous  for  this  factor  give  the  ''selected  group."  Those 
heterozygous  for  it  or  lacking  it  altogether  give  the  atavistic  or  original 
group. 

(3)  Since  in  every  one  of  the  24  generations  of  this  experiment  the 
gene  for  Notch  is  in  a  heterozygous  condition  an  extraordiiuirily 
favorable  chance  exists  for  contamination  of  the  Notch  genes,  if  such  a 
thing  is  possible.  Were  it  possible  the  results  of  the  selection  might  be 
supposed  to  be  due  to  an  influence  of  the  normal  gene  on  the  Notch 
gene.  Mass  selection  was  practiced  in  the  same  direction  that  such  a 
supposition  would  lead  to.  That  the  result  wat>  not  re^iched  in  this 
way  is  showai  not  only,  as  stated  above,  through  the  demonstration  of 
the  specific  modifier  involved,  but  also  by  out-cros.sing;  for  if  at  any 
time  the  selected  Notch  females  (even  those  not  showing  any  Notch  at 
all)  are  bred  to  flies  of  almost  any  wild  stock,  the  atavistic  Notch  is  n^ 
covered  in  the  first  generation.  Here,  ow4ng  to  the  dominance  of  the 
character,  one  can  obviate  completely  the  difficulty  that  Castle  met 
with  w^hen  studying  the  influence  of  selection  on  a  recessive  cluiractor. 
Castle  was  obliged  to  out-cross  his  rats  and  then  inbrecd  the  Fi.  The 
chance,  unless  guarded  against  scrui^ulouslj',  of  introducing  new 
genes  into  the  result  is  ever  present  under  such  conditions  an- 1  >\'»'< 


..... 

■  • 


388  GENES   MODIFYING   NOTCH. 

not  appear  to  have  been  avoided  by  Castle,  hence  his  appeal  to  con- 
tamination of  genes  to  help  him  out  of  an  apparent  contradiction.  In 
the  present  case  of  Drosophila  the  experiment  is  of  a  kind  to  demon- 
strate cleariy  whether  contamination  had  occurred  or  not,  and  the 
results  clearly  show  that  it  did  not  occur,  even  under  the  unusually 
favorable  opportunities  that  heterozygosis  for  24  generations  offered. 

(4)  A  modification  of  the  Notch  character  appeared  several  times  in 
the  course  of  the  work.  This  variation,  called  short  Notch  (fig.  94,  &,), 
is  in  the  opposite  direction  from  the  selected  type  ''produced  by 
selection."  By  proper  tests  it  is  shown  that  this  variation  is  due  to 
another  modifying  gene  situated  in  the  X  chromosome  itself.  When  in 
homozygous  condition  the  gene  shortens  and  broadens  the  Notch  wing, 
producing  a  greater  amount  of  curvature  at  the  end.  This  variant, 
too,  can  be  brought  back  at  any  time  to  the  original  or  atavistic  type 
by  breeding  to  wild  flies. 

(5)  In  the  course  of  the  work  a  number  of  other  mutations  occurred, 
some  of  which  modified  the  -wing  in  somewhat  the  same  way  as  the 
Notch  gene  itself  (nick  and  cut),  others  modified  the  wing  as  domi- 
nants (truncate),  or  in  the  homozygous  condition  (deformed  eyes,  etc.). 
Other  modifications  causing  serrations  or  notchings  on  the  end  of  the 
wings  are  known  in  Drosophila;  the  location  of  these  genes  in  other 
chromosomes  or  at  other  levels  than  Notch  in  the  X  chromosome 
shows  that  they  are  different  from  Notch.  Were  it  not  possible,  as  it 
is  in  this  case,  to  check  up  such  modifications  that  resemble  somewhat 
the  character  under  selection,  one  might  easily  be  led  to  entirely 
erroneous  deductions. 

(6)  In  the  course  of  the  experiment  two  females  appeared  with 
exceptional  sex  ratios,  viz,  76  9  to  1  cf  and  119  9  to  10  d^.  Their 
occurrence  is  undoubtedly  due  to  the  appearance  of  a  lethal  in  the 
''normal"  X  chromosome  of  the  Notch  mother,  because  in  several 
cases  such  changes  in  the  sex-ratio  in  Drosophila  have  been  shown  to 
be  due  to  such  a  situation.  In  consequence  of  two  lethals  in  the 
mother,  one  in  each  X  chromosome,  every  son  will  die,  except  for  an 
occasional  cross-over  that  will  give  rise  to  a  normal  son.  That  this 
result  is  not  due  to  the  production  of  a  homozygous  Notch  female  by 
non-disjunction  is  demonstrated  by  the  kind  of  daughters  produced, 
which  were  half  normal,  half  Notch.  All  must  have  been  Notch  if  the 
mother  had  been  a  double  lethal  Notch  female  (XXY). 


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I 


DATE  DUE 


GAYLORD 

PRINTED  IN  U.S.A. 

"59^.7015 
C289c 

Carnepie  Institution  of  Washington 
Contributions  to  tK^  """ 


melanogaster 


DEC  1  7   ^369 


595.7015 
C289c 

Carnegie  Institution  of  l^shington 


Contributions  to  the  genetics  of 
Droscphila  melanogaster 


'.  '■"■fshi 


>';■'■  '■/ 


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